Node having an adaptive space-spectrum whiteniner and multi-user rake receiver for use in a cooperative broadcast multi-hop network that employs broadcast flood routing and multi-hop transmission with cooperative beamforming and adaptive space-spectrum whitening

ABSTRACT

A node is provided for a cooperative broadcast multi-hop network that employs broadcast flood routing and multi-hop transmission. The node includes antennas and a waveform module having a receiver processing chain that can include an adaptive space-spectrum whitener (ASSW) module and a multi-user RAKE (mRAKE) receiver. Each antenna can receive output a channel that includes direct-sequence spread-spectrum signals received from other nodes and multi-path components of those transmissions. The ASSW module can perform adaptive space-spectrum whitening to detect and remove interference signals received from each of the channels by performing a covariance analysis to generate channelized signals. The ASSW module can include modified Discrete Fourier Transform (MDFT) analysis and synthesis modules that generate an interference mitigated time-domain channelized signals. The mRAKE receiver, when performing demodulation processing, can combine the interference mitigated time-domain channelized signals to generate fingers that combine components of transmissions received from the other nodes.

TECHNICAL FIELD

The present invention generally relates to wireless communicationsystems, and more particularly relates to cooperative broadcastmulti-hop network that employs broadcast flood routing and multi-hoptransmission using a direct-sequence spread-spectrum (DSSS) waveformwith cooperative beamforming and adaptive space-spectrum whitening. Anode, that is part of the cooperative broadcast multi-hop network, isdisclosed. The node includes antenna(s) that can each output a channelthat includes DSSS signals received from other nodes and multi-pathcomponents of those transmissions, and a waveform module having areceiver processing chain that can include an adaptive space-spectrumwhitener (ASSW) module can perform adaptive space-spectrum whitening todetect and remove interference signals received from each of thechannels by performing a covariance analysis to generate channelizedsignals, and a multi-user RAKE (mRAKE) receiver. The ASSW module caninclude modified Discrete Fourier Transform (MDFT) analysis andsynthesis modules that generate an interference mitigated time-domainchannelized signals. The mRAKE receiver, when performing demodulationprocessing, can combine the interference mitigated time-domainchannelized signals to generate fingers that combine components oftransmissions received from the other nodes.

BACKGROUND

In recent years, the U.S. Department of Defense (DOD) has sought todevelop RF communications technologies that protect signals from enemyattempts to detect, intercept, or exploit those signals, while stillmaintaining other desirable attributes and capabilities of thecommunication systems (e.g., throughput, spectral efficiency, networkperformance, latency, etc.).

One such example is the U.S. Defense Advanced Research Projects Agency's(DARPA's) Computational Leverage Against Surveillance Systems (CLASS)program that is designed to help safeguard military ground-to-ground,ground-to-air, and air-to-air RF communications. A goal of the DARPACLASS program is to create new waveforms and technology to protectmilitary RF communications from enemy signals intelligence. The DARPACLASS program sought to create communications waveforms that capitalizeon advanced in digital signal processing to enable future militarycommunications systems to receive and process transmissions usingsophisticated application specific integrated circuits (ASICs) whileforcing adversaries to require supercomputer processing to intercept andexploit radio signals.

Resilience in electronic warfare (EW) environments is provided throughwaveform complexity, spatial diversity techniques and interferenceexploitation. Waveform complexity refers to removing predictablestructures from communication waveforms, adding atypical randomstructure, new ways to acquire and track signals, and similartechniques. Waveform complexity uses advanced communications waveformsthat are difficult to recover without knowledge and understanding of thesignals itself. Spread-spectrum communications are signal structuringtechniques in which telecommunication signals transmitted in a band isconsiderably larger than the frequency content of the originalinformation. A receiver correlates receive signals to retrieve theoriginal information signal. There are many types of spread-spectrumcommunication systems including, but not limited to, direct-sequence,frequency hopping, and hybrid variations that combine these techniques.Regardless of the variation, each of these techniques utilizespseudorandom number sequences to determine and control a spreadingpattern of a signal across an allocated bandwidth. Any of thesespread-spectrum communication systems can help prevent adversaries fromjamming communications and thus provide anti jamming capability. Forexample, direct-sequence spread-spectrum (DSSS) is employed for lowprobability of intercept/low probability of detection (LPI/LPD)signaling. In addition, these types of spread-spectrum communicationsystems, can also be used to hide the fact that communication was eventaking place. This is sometimes referred to as low probability ofintercept or LPI.

Spatial diversity transmission refers to manipulating the spatialcharacteristics of a signal to create controlled, recoverable waveformsat the destination receiver while creating difficult-to-recover signalcharacteristics at other locations. Spatial diversity uses distributedcooperative communications devices and the communication environment todisguise and dynamically vary the apparent location of the signal. Whenspatial antennas are co-located together (e.g., in a single unit orbox), or when the antennas are stationary and connected to a centraldistribution point, it can be relatively easy to implement transmitspatial diversity. However, in other applications, implementing transmitspatial diversity becomes significantly more challenging. For example,when the transmitters are non-collocated (e.g., separate terminals),dynamically moving, and lack centrally controlled coordination, thecoordination required across the devices becomes more challenging. Thedisclosed embodiments can allow spatial diversity and coherent combiningto be employed with reasonable complexity.

Interference exploitation or spectrum obfuscation makes use of theclutter in the signal environment to make it difficult for an adversaryto isolate a particular signal. Interference exploitation techniquesseek to use natural and artificial interference against an unintendedreceiver (e.g., to force adversaries to dedicate processing resources tothe source signal to reduce interference).

Cooperative broadcast transmitters and receivers are typically complex.Scalability becomes a challenge with dynamic or growing network users.Some of the challenges faced include processing multi-user detection,estimation of channel state information for each received user-channelfor beam combining, or coordination of space time block codes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIGS. 1A and 1B are diagrams of a communication system in accordancewith the disclosed embodiments, where FIG. 1A illustrates one example ofuplink operation of the communication system and where FIG. 1Billustrates one example of downlink operation of the communicationsystem;

FIG. 2 is a block diagram of a dismount node in accordance with thedisclosed embodiments;

FIG. 3A is a block diagram of a software-defined waveform module of adismount node in accordance with the disclosed embodiments;

FIG. 3B is a block diagram that illustrates one non-limitingimplementation of a portion of a receiver processing chain of FIG. 3A inaccordance with one implementation of the disclosed embodiments;

FIG. 4 is an exemplary functional block diagram of a mounted node inaccordance with the disclosed embodiments;

FIG. 5 is a block diagram of a software-defined waveform module of amounted node in accordance with the disclosed embodiments;

FIG. 6 is a block diagram that illustrates further details of oneembodiment of the adaptive space-spectrum whitener of FIG. 5 inaccordance with the disclosed embodiments; and

FIG. 7 is a table that shows waveform attributes for a range of modesand throughput options that are supported in accordance with somenon-limiting examples of the disclosed embodiments.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding background or the following detaileddescription.

The disclosed embodiments relate to a cooperative broadcast, CDMA-basedmulti-hop network with adaptive, scalable, non-collocated cooperativebeamforming techniques, and adaptive space-spectrum whitening. Themulti-hop network employs broadcast flood routing and multi-hoptransmission. The originator of a communication that is the messagesource of a broadcast message, also referred to herein as an“originating node” or “source message node,” can transmit on oddnumbered hop intervals, and any nodes that receive that communicationerror-free can then serve as relay nodes that retransmit thecommunication on even numbered hop intervals. A receive node can beeither a relay node or listener node. Relay nodes, which received themessage on odd hop numbered hop intervals, can re-broadcast or relay theerror-free packets on even hop numbered hop intervals. Any nodes that donot receive the original communication error-free are listener nodes,also referred to herein as destination nodes. The listener nodes canreceive the communications transmitted by the relay nodes. A listenernode receives on even numbered hop intervals during the active messageinterval. In one implementation, a listener node can do both (e.g.,receive on odd numbered hop intervals and on even numbered hop intervalsduring the active message interval). For larger networks with greatergeographic coverage, this process can be extended by repeating themessage over additional odd/even hops.

In one embodiment, cooperative beamforming is employed on both uplinkand downlink communications. For uplink communications coherentcombining is employed. To implement distributed/cooperative beamforming,each node in the network is assigned its own unique scramble code thatcan be used to identify that node. For instance, each unique scramblecode can be a pseudo noise (PN) code that is used to spread a basebandsignal over a broader frequency band in accordance with a pseudorandombit sequence during transmission. The unique scramble codes allow areceiving node to separate and distinguish between individualtransmissions that are received from other nodes that are part of thenetwork. In one embodiment, a user or node identifier is determined byits scramble sequence. For example, in one implementation, the scramblecode can be a Kasami code that is applied after spreading has occurredusing a spreading code, i.e. on a chip basis. This is a uniqueassignment to each user node and permits a receiver to distinguishbetween the multiple transmitting nodes. In addition, a random scramblecode (e.g. TRANSEC or AES sequence) can also be applied that is commonacross all nodes and changes on a per hop basis. As such, this randomscramble code provides inherent timing information on a hop-by-hopbasis. Each node includes a multi-user rake receiver and a beamformingmodule. Each node can receive transmissions from multiple transmitternodes (e.g., within the same RAKE reception window), and then implementscooperative beamforming using the received transmissions and eachmultipath component for each of the received transmissions. In oneembodiment, each node employs adaptive space-spectrum whitening for antijam and interference mitigation.

Prior to describing the disclosed embodiments, a brief summary will beprovided to describe modulation and channel access technologies that areused is some embodiments of a cooperative broadcast multi-hop networkwill now be provided.

Spread-Spectrum

Spread-spectrum modulation techniques have been adopted for many currentand future military communication systems to accommodate high data rateswith high link integrity, even in the presence of significant multipatheffects and interfering signals. In telecommunications, the term“spread-spectrum” is defined as any of a group of modulation techniquesor formats in which a radio frequency (RF) bandwidth much greater thannecessary is used to transmit an information signal so that asignal-to-interference improvement may be gained. The energy containedin a baseband signal is spread over a broad-band in a pseudo-randommanner during transmission and the narrow-band signal is retrievedduring reception. The spreading method for spreading a given signal isprovided by the modulation scheme that is utilized.

Spread-spectrum transmission offers many advantages over afixed-frequency transmission. Spread-spectrum signals are highlyresistant to narrowband interference. The process of re-collecting aspread signal spreads out the interfering signal, causing it to recedeinto the background. Spread-spectrum signals are difficult to intercept.A spread-spectrum signal may simply appear as an increase in thebackground noise to a narrowband receiver. An eavesdropper may havedifficulty intercepting a transmission in real time if the pseudorandomsequence is not known. Spread-spectrum transmissions can share afrequency band with many types of conventional transmissions withminimal interference. The spread-spectrum signals add minimal noise tothe narrow-frequency communications, and vice versa. As a result,bandwidth can be used more efficiently. Spread-spectrum signals are alsohighly resistant to deliberate jamming, unless the adversary hasknowledge of the spreading characteristics.

Direct-Sequence Spread-Spectrum (DSSS)

DSSS is a form of spread-spectrum modulation used to reduce overallsignal interference, where a code sequence is used to directly modulatea carrier. The spreading of this signal makes the resulting widebandchannel noisier, allowing for greater resistance to unintentional andintentional interference. To explain further, in DSSS communications, amessage signal is used to modulate a bit sequence known as a pseudonoise (PN) code, also called a pseudo-random digital sequence, generatedby a pseudo-random code generator. This PN code consists of a radiopulse that is much shorter in duration (larger bandwidth) than theoriginal message signal. In this context, the duration of the radiopulse for the PN code is referred to as the chip duration. The “chip”rate is much higher than the symbol rate of the signal beingtransmitted. The smaller this duration, the larger the bandwidth of theresulting DSSS signal. For example, a transmitter modulates the carrierwith the PN code. Each symbol of the original message signal isindividually encoded by multiple chips per symbol (e.g., typically 32 to512 chips per symbol.) A receiver demodulates the carrier so as todecode the information signal by adjusting the phase of a PN code,generated by a local PN code generator and identical to the transmittedPN code, to correlate (or “synchronize”) with the transmitted PN code.For proper despreading of the digital information to occur, the locallygenerated PN code must exactly align with the transmitted PN code, inparticular by taking into account the shift in phase due to delay ofreception resulting from the finite speed of electromagnetic wavepropagation. This modulation of the message signal scrambles and spreadsthe pieces of data, and thereby resulting in a bandwidth size nearlyidentical to that of the PN code.

Code Division Multiple Access (CDMA)

CDMA is a channel access method used by various radio communicationtechnologies. CDMA is an example of multiple access, where severaltransmitters can send information simultaneously over a singlecommunication channel. This allows several users to share a band offrequencies. To permit this without undue interference between theusers, CDMA employs spread-spectrum technology and a special codingscheme where each transmitter is assigned a unique scramble code. Eachuser in a CDMA system uses a different code to modulate their signal.The best performance occurs when there is good separation between thesignal of a desired user and the signals of other users. The separationof the signals is made by correlating the received signal with thelocally generated code of the desired user. If the received signalmatches the desired user's code, then the correlation function will behigh and the system can extract that signal. If the desired user's codehas nothing in common with the signal, the cross-correlation should beas close to zero as possible (thus eliminating the signal). If the codeis correlated with the signal at any time offset other than zero, thecorrelation should be as close to zero as possible. This is referred toas auto-correlation and is used to reject multi-path interference.

Frequency Hopping DSSS (FH/DSSS)

The performance of any radio communication system is affected by severalfactors such as: interference, and jamming caused by some other parallelnetworks for the purpose of decreasing the performance of a givensystem. To address these problems, DSSS signaling is combined with theuse of coordinated frequency hopping (FH) modulation to provide hybridspread-spectrum (HSS) transmission scheme. As used herein, the term“hybrid spread-spectrum (HSS)” can refer to a combination of DSSS, forexample, code division multiple access (CDMA), and at least one offrequency hopping, time hopping, time division multiple access (TDMA),orthogonal frequency division multiplexing (OFDM) and/or spatialdivision multiple access (SDMA). DSSS generates a sequence of bits andspreads the spectrum with a PN code or “spreading sequence,” while FHSSsends the data into different channels with variable data rates. Thehybrid DS/FH approach takes advantage of DSSS and uses it in multiplechannels.

In one embodiment, a cooperative broadcast multi-hop network is providedthat employs broadcast flood routing and multi-hop transmission using adirect-sequence spread-spectrum (DSSS) waveform. The cooperativebroadcast multi-hop network includes a plurality of nodes. In oneembodiment, the DSSS waveform can be a frequency-hopping direct-sequencespread-spectrum (FH/DSSS) waveform in which DSSS modulation is combinedwith frequency hopping (FH) between DSSS channels to provide a hybridFH/DSSS modulation format. In one implementation, the FH/DSSS waveformhas a hop rate and a spreading rate that are adjustable. Each node cantransmit transmissions that are modulated using a unique scramble codefor that node that identifies transmissions from that node (todistinguish them from transmissions by other nodes) and a commonscramble code that is shared with the other nodes. For example, in oneembodiment, the unique scramble code is a first code that is unique forthat particular node that is logically combined with a security code. Inone embodiment, each transmission by a node is a direct-sequencespread-spectrum (DSSS) signal having DSSS waveform. Each of the nodescan broadcast transmissions on a unique channel for that node whentransmitting as an original sender of a transmission, and receivetransmissions from nodes that are original senders and multipathcomponents thereof on the odd numbered hop intervals. The unique channelfor each node is defined by an odd numbered hop interval assigned tothat node and the unique scramble code assigned to that node. Each ofthe nodes can re-transmit, when operating as a relay node, anytransmissions that are received error free from other nodes on anotherunique channel for that node that is defined by an even numbered hopinterval assigned to that node and the unique scramble code assigned tothat node, and receive re-transmitted transmissions from nodes that arerelays and multipath components thereof on the even numbered hopintervals. In one embodiment, each node can include a differentinterleaver module than the other nodes.

In one embodiment, each of the nodes includes at least one antennaconfigured to receive a plurality of DSSS signals from other nodes on aparticular channel, and output a channel that includes the plurality ofDSSS signals. The plurality of DSSS signals can include transmissionsthat are directly received from other nodes and multi-path components ofthose transmissions.

In one embodiment, each of the nodes includes a waveform module having areceiver processing chain. Each receiver processing chain can include amulti-user RAKE receiver that can combine, when performing demodulationprocessing, a plurality of transmissions directly received from othernodes and multipath components of transmissions received from othernodes. In one implementation, each multi-user RAKE receiver can includefirst and second correlation modules each being configured to receivechannelized signals output by an adaptive space-spectrum whitener (ASSW)module, and a finger selection module. Each channelized signal can be aspatial stream. For example, each of the first and second correlationmodules can include correlator blocks for each of the plurality of nodes(1, . . . , N). Each correlator block is driven by a unique scramblecode that identifies transmissions from a particular node and performscorrelation for that particular node by processing a spatial streamreceived from the ASSW module and the unique scramble code for thatparticular node to determine channel-multipath correlations and generateone or more candidate fingers multipath location and respective complexweight. Each finger corresponds to a specific channel-signal pair forthat particular node or a specific channel-multipath component pair forthat particular node. The finger selection module can receive thefingers output from each correlator block and to select a subset (1 . .. F) of the fingers having sufficient correlation by selecting whichnodes contribute to the F total largest signal multipath componentsreceived.

In one embodiment, a maximum likelihood ratio combiner module isprovided that includes a plurality of processing modules and a maximumlikelihood ratio combiner module. Each processing module processessignals for that node. Each processing module can include a coherentcombine module for that node, a descrambler for that node, and a pilotdespreader module for that node. Each coherent combine module canreceive a number of the subset of fingers from the finger selectionmodule, and coherently combine that number of the subset of fingers togenerate an output signal. Each descrambler can descramble the outputsignal received from that coherent combine module using a uniquedescramble code for that node to generate a descrambled signal, and eachpilot despreader module can despread the descrambled signal to generatea despread pilot signal.

In one embodiment, the receiver processing chain in each waveform modulefor each of the nodes can include a maximum likelihood ratio combinermodule that includes a coherent combiner module that can coherentlycombine, using pilot soft-decision bits from each of the despread pilotsignals for each node, each of the descrambled signals received acrossmultiple nodes to generate a coherently constructed signal of spreaddata channels that comprise a coherently combined vector of chips ofinformation.

In one embodiment, the receiver processing chain in each waveform modulefor each of the nodes can include a data despreader module and a gather,de-interleave and decoder block. Each data despreader module candespread and convert the chips from the respective data channels togenerate demodulated data symbols that are converted into datasoft-decision bits. Each gather, de-interleave and decoder block caninclude a gather block configured to concatenate the data soft-decisionbits from each hop across multiple received hops together to formcodeword soft-decision bits; a de-interleaver block configured tode-interleave the codeword soft-decision bits; and a decoder blockconfigured to perform low density parity check (LDPC) forward errorcorrection (FEC) decoding and broadcast decoding on the codewordsoft-decision bits to recover information bits corresponding to thecomplete codeword.

In one embodiment, the receiver processing chain in each waveform modulefor each of the nodes can include a maximum likelihood ratio combinermodule that can maximally ratio combine aligned symbols for each of asubset (1 . . . F) of the fingers on a per channel basis to generate asoft decision across each of the multiple channels, and combine the softdecisions into a joint soft decision.

In one embodiment, the antenna is a first antenna, and one or more ofthe plurality of nodes can include a second antenna configured toreceive a second plurality of DSSS signals from other nodes on a secondparticular channel, and output a second channel that includes the secondplurality of DSSS signals, wherein the second plurality of DSSS signalsinclude transmissions that are directly received from other nodes andmulti-path components of those transmissions.

In one embodiment, the receiver processing chain of each node furthercan include a de-hop module and an adaptive space-spectrum whitener(ASSW) module. Each de-hop module can de-hop each of the received DSSSsignals by tuning to a particular frequency to receive each DSSS signaland then channelizing input spectrum for each of the received DSSSsignals to generate beam samples for each channelized signal. Each ASSWmodule can perform adaptive space-spectrum whitening to detect andremove interference signals received from each of, for example, thefirst and second channels by performing a covariance analysis togenerate a first channelized signal that comprises transformed beamsamples for the first channel and a second channelized signal thatcomprises transformed beam samples for the second channel. Each ASSWmodule can output the first and second channelized signals to first andsecond correlation modules of the multi-user RAKE receiver of thatdismount node.

In one embodiment, each ASSW module can include a modified DiscreteFourier Transform (MDFT) analysis module, an adaptive interferencemitigation space-frequency whitener module, and a MDFT synthesis module.

Each modified Discrete Fourier Transform (MDFT) analysis module caninclude a plurality of an MDFT analysis banks. Each MDTF analysis bankcorresponds to an antenna and can receive a beam from an antenna in thespectral domain and channelize the beam to generate a channelized beamof frequency samples. Each beam comprises a digitized spatial stream offrequency channelized RF samples that are digitized to preserve spatialdiversity. Each channelized beam comprises multiple spectral channels.The channelized beams collectively comprise a number of spectral-spatialchannels equal to the product of the number of channelized beams and themultiple spectral channels. The channelized beams collectively form aspatial-spectral matrix (Z) of time-frequency samples across thedifferent antennas. The adaptive interference mitigation space-frequencywhitener module can apply a whitening matrix (W) to the spatial-spectralmatrix (Z) to remove interference and generate an interference-mitigatedwhitened matrix (WZ) that comprises a plurality ofinterference-mitigated spatial-spectral domain channels. Each MDFTsynthesis module can include a plurality of MDFT synthesis banks thatcollectively re-construct the interference-mitigated whitened matrix(WZ) back to a time-domain matrix (Y) that comprises interferencemitigated time-domain channelized signals. Each MDFT synthesis bank isconfigured to perform a MDFT synthesis operation on one of thespatial-spectral domain channels to generate an interference mitigatedtime-domain channelized signal of reconstructed beam samples. Eachinterference mitigated time-domain channelized signal represents arespective spatial channel. Each row of the spatial-spectral matrix (Z)represents spatial-spectral samples unique to one of the channelizedbeams, and each column of the spatial-spectral matrix (Z) representstime indices. In one embodiment, the adaptive interference mitigationspace-frequency whitener module calculates auto-correlation matricesacross rows of the spatial-spectral matrix (Z) such that the resultingwhitened matrix (WZ) is a diagonal correlation matrix.

In one embodiment, each waveform module can include a maximum likelihoodratio combiner module that along with the multi-user RAKE receivercollectively provides a multi-channel beamformer module. Themulti-channel beamformer module can perform cooperative beamforming on aper channel basis by processing the time-domain matrix (Y) andcoherently combine a subset of transmissions and multipath componentsfor each transmission that are received from other nodes together. Thesubset of transmissions and multipath components are those having signalstrength greater than or equal to a threshold. In this embodiment,coherently combining is accomplished by time aligning the respectivesignals of interest, and removing frequency offset and phase offset fromeach transmission.

In one embodiment, the multi-channel beamformer module is configured to:receive the interference mitigated time-domain channelized signals fromeach MDFT synthesis bank; derive a joint code-based-beamforming matrix(B) across all detected interference mitigated time-domain channelizedsignals; apply the joint code-based-beamforming matrix to thetime-domain matrix to beam combine the interference mitigatedtime-domain channelized signals; and select a sub-set of theinterference mitigated time-domain channelized signals to generate abeam combined signal.

In one embodiment, at least one of the plurality of nodes further caninclude a third antenna and a fourth antenna. The first, second, thirdand fourth antennas are part of a multi-band phased antenna array havinga number (N) of antennas that include the first, second, third andfourth antennas. In one implementation, the third antenna can receive athird plurality of DSSS signals from other nodes on a third particularchannel, and output a third channel that includes the third plurality ofDSSS signals. The fourth antenna can receive a fourth plurality of DSSSsignals from other nodes on a fourth particular channel, and output afourth channel that includes the fourth plurality of DSSS signals. Thethird and fourth plurality of DSSS signals each include transmissionsthat are directly received from other nodes and multi-path components ofthose transmissions. In this embodiment, the receiver processing chainof the waveform module further can include a space-time receivecode-based beamforming module that includes a multi-channel beamformermodule, a multi-user RAKE receiver and a maximum likelihood ratiocombiner module. The multi-channel beamformer module can performadaptive beamforming on a per channel basis. In one embodiment, themulti-channel beamformer module performs a matrix operation thatlinearly transforms interference mitigated time-domain channelizedsignals to coherently combine the interference mitigated time-domainchannelized signals into a smaller number (NT) of directional beams. Themulti-user RAKE receiver can process each of the directional beamsoutput by the multi-channel beamformer module and align symbols usingscramble code correlation. In one implementation, the multi-channelbeamformer module can receive the interference mitigated time-domainchannelized signals from each MDFT synthesis bank; derive a jointcode-based-beamforming matrix (B) across all detected interferencemitigated time-domain channelized signals; apply the jointcode-based-beamforming matrix to the time-domain matrix to beam combinethe interference mitigated time-domain channelized signals; and select asub-set of the interference mitigated time-domain channelized signals togenerate a beam combined signal. The transmissions received across eachof the number (N) of antennas of the multi-band antenna array arecoherently combined on a per channel basis to generate a correspondingdirectional beam. Each directional beam can cover a portion of anazimuth range.

In one embodiment, each of the nodes includes a power control modulethat is configured to: encode originating transmit power in a message tosupport adaptive power control and encode channel status information inthe message so that channel status of the cooperative broadcastmulti-hop network is propagated to each of the other nodes. Each node,when transmitting as an original sender of a transmission, can broadcasta particular message on odd numbered hop intervals to propagate theoriginating transmit power channel status information to other nodes inthe cooperative broadcast multi-hop network. In one implementation, theparticular message can be a push-to-talk (PTT) message or asynchronization message that is regularly broadcast a synchronizationchannel (used to maintain time synchronization relative to a master nodeso that transmissions of the nodes are synchronized to arrive within thesame reception window of the multi-user RAKE receiver). Each node thatreceives the particular message can process the channel statusinformation to estimate a receive signal-to-noise (SNR); determine,based on the estimated receive SNR and the originating transmit power,whether transmit power of that node should be adjusted beforetransmitting or relaying a message; and when it is determined thattransmit power of that node is to be adjusted: adjust current transmitpower of that node; and re-transmit messaging including current transmitpower on even numbered hop intervals.

In one embodiment, each node can include a beamformer and hop assignmentmodule that includes a beamformer module and a hop assignment module.The hop assignment module includes a Fast-Frequency Hopping (FFH)transmitter that is configured to assign a hop number for transmissionsby that node, where a hop number is a function of time, and a hopfrequency is based on pseudo-random sequence. The beamformer module canupdate amplitude and phase weightings of a DSSS signal that is providedto the two or more antennas.

Having given this overview a communication system in accordance with thedisclosed embodiments will now be described with reference to FIGS. 1Aand 1B. FIGS. 1A and 1B are diagrams of a communication system 100 inaccordance with the disclosed embodiments. The communication system 100can also be referred to as a squad local area network. The communicationsystem 100 includes a plurality of dismount nodes 110-1 . . . 110-8 andat least one mounted node 120, which can also be referred to herein as amounted destination node or mounted listener node. In this non-limitingembodiment, dismount nodes 110-1, 110-2, 110-4, 110-5, 110-6, 110-7,110-8 are carried by ground personnel, while dismount node 110-3 ismounted on a drone or other airborne machine to enable range extensionand provide enhanced coverage (e.g., reliable coverage withinchallenging terrain and foliage), whereas the mounted node 120 ismounted on a ground vehicle. Given the small size and low power of thedismount nodes, a dismount node 110-3 can be hosted on a drone toprovide one or more aerial relay nodes, dramatically improving linkperformance. The mounted node 120 (with more antennas and moreprocessing) extends the range of a protected Low Probability ofIntercept/Low Probability of Detection (LPI/LPD) waveform withoutincreasing the transmitted power of the dismount nodes 110-1 . . .110-8, while maintaining LPI/LPD performance.

The various nodes 110, 120 communicate with each other using theprotected LPI/LPD waveform to provide scalable anti-jam, LPI/LPD andthroughput. The protected LPI/LPD waveform is also designed to allow forlong battery life. In one embodiment, the LPI/LPD waveform is adirect-sequence spread-spectrum (DSSS) waveform that utilizes a DSSSmodulation format. In another embodiment, DSSS modulation is combinedwith frequency hopping (FH) between DSSS channels to provide a hybridfrequency-hopping direct-sequence spread-spectrum (FH/DSSS) waveformhaving a FH/DSSS modulation format. The FH/DSSS waveform has a hop rateand a spreading rate that are adjustable. FH is power efficient methodto achieve a high detection ratio, and also allows for a selectable hoprate to optimize LPD detection ratio, or throughput with single carrieroperation. In one embodiment, the FH/DSSS waveform combines hybridFH/DSSS with CDMA to provide an odd/even numbered hop intervalcooperative broadcast, multi-hop flooding network in a manner thatallows for diversity gains approaching coherent transmit beamforming. FHcan be used as the multiple access method in a CDMA scheme to providefrequency hopping-code division multiple access (FH-CDMA). In anotherembodiment, time hopping is also used with and without frequency hoppingso that the interval between transmissions is pseudo randomly changed.

This frequency-hopping direct-sequence spread-spectrum scheme can helpprovide frequency diversity and allows the data transmission to betterwithstand deleterious path effects such as narrow-band interference,jamming, fading, and so on, while also reducing multipath interference.Each available frequency band is divided into sub-frequencies. Data istransmitted on different frequency sub-bands or sub-carriers indifferent time intervals, which are also referred to as “hop periods,”where the data transmission rapidly changes (“hops”) among thesefrequency sub-bands in a predetermined order (i.e., the datatransmission hops from sub-band to sub-band in a pseudo-random manner).In other words, the radio signals are transmitted by rapidly switching acarrier among many frequency channels, using a pseudorandom sequenceknown to both transmitter and receiver. When the hopping patterns arechosen carefully, adjacent channel interference can also be minimized. Asignaling channel is used to assign frequency hopping patterns to activeuser-pairs to avoid co-channel interference. This enables the assignedfrequency band to be fully utilized.

In one embodiment, a CDMA-based cooperative broadcast multi-hop networkcan be provided in which dismount nodes can receive downlinktransmissions from multiple of the other nodes on separate CDMAchannels, and mounted node(s) can receive uplink transmissions from atleast some of the dismount nodes on separate CDMA channels. The CDMAwaveform allows for robust beamform combining through use of separateCDMA “channels” for each user with continuous link-channel informationon all connections. As will be described below, beamforming can beimplemented on a per link basis (e.g., versus aggregate basis).

Each node 110, 120 is assigned its own scramble code for generatingcommunications sent to other nodes 110, 120. The multiple-accesscommunication system can simultaneously support communication formultiple nodes. Each dismount node 110-1, 110-2, 110-3, 110-4, 110-5,110-6, 110-7, 110-8 is capable of communicating with other dismountnodes via relay links, and is capable of communicating with at least onemounted node 120 via transmissions on uplinks 130 and downlink 140-H.The downlink (or forward link) refers to the communication link from themounted node 120 to the dismount nodes 110-1, 110-2, 110-3, 110-4,110-5, 110-6, 110-7, 110-8, and the uplink (or reverse link) refers tothe communication link from the dismount nodes 110-1, 110-2, 110-3,110-4, 110-5, 110-6, 110-7, 110-8 to the mounted node 120. As will nowbe explained, an odd/even numbered hop interval broadcast flood routingprotocol helps ensure highly reliable message delivery and minimizesspectrum usage.

Uplink Communications by Dismount Nodes: Sender Dismount Node and RelayDismount Nodes

During uplink operation, one of the dismount nodes acts as a senderdismount node (i.e., the node that is the originator of the uplinkcommunication that is intended for the mounted node 120). The senderdismount node transmits an uplink communication on odd numbered hopintervals. All of the other dismount nodes can act as relay dismountnodes, where each relay dismount node, that receives the uplinkcommunication (error free) from the sender dismount node, attempts torelay that uplink communication to the mounted node 120 on even numberedhop intervals.

FIG. 1A illustrates one example of uplink operation of the communicationsystem 100 of the communication system 100 in accordance with thedisclosed embodiments. As will be explained in greater detail below,when operating as a sender/originator of an uplink communication, eachdismount node 110-1, 110-2, 110-3, 110-4, 110-5, 110-6, 110-7, 110-8 cancommunicate (transmit) their uplink communications to the mounted node120 (and other dismount nodes) on odd numbered hop intervals (or “oddfrequency hops”). By contrast, when operating as a relay, each dismountnode 110-1, 110-2, 110-3, 110-4, 110-5, 110-6, 110-7, 110-8 can relay orre-transmit uplink communications (received from a sender dismount node)to the mounted node 120 on even numbered hop intervals (or “evenfrequency hops”). In other words, these re-transmissions for floodrouting occur on even numbered hop intervals. By isolating the originaltransmission on odd numbered hop intervals and re-transmissions on evennumbered hop intervals, this prevents “message blow back” (e.g., theoriginating transmitter (sender node) and relay nodes do not receivere-transmissions). This reduces complexity and network self-inducednoise.

In this example, during uplink operation odd-even numbered hop intervalflood routing is observed, and the sender dismount node 110-8 broadcastsa communication/message on odd numbered hop intervals over a channel130-A using a shared Transmission Security Key (TRANSEC) scramble codethat the sender and receiver share in advance and a unique scramble codeA that identifies the sender dismount node 110-8 and can thus be used byother nodes to distinguish transmissions from the sender dismount node110-8. The communication/message from the sender dismount node 110-8 canpotentially be received by one or more of the various relay dismountnodes 110-1 . . . 110-7 and the mounted node 120.

Each of relay dismount nodes 110-1 . . . 110-7 can function as a relaynode that relays the communication/message from sender dismount node110-8 back towards the mounted node 120 using its own unique channelthat is defined by a hop assignment (even numbered hop intervals) and aunique scramble code for that relay dismount node 110-1 . . . 110-7. Inone embodiment, each of the dismount nodes 110-1 . . . 110-7 thatreceive a code word error free can re-broadcast the code word on evennumbered hop intervals, with each device/node 110 using their uniquescramble code assignment along with a common shared spreading code.Relay dismount nodes that did not receive the code word error free andthe sender dismount node 110-8, listen to these even numbered hopintervals. As used herein, the term “code word” can refer to an elementof a standardized code or protocol. Each code word is assembled inaccordance with the specific rules of the code and assigned a uniquemeaning.

For example, in this non-limiting example, relay dismount node 110-1relays the communication/message over a channel 130-C on even numberedhop intervals using scramble code C, relay dismount node 110-2 relaysthe communication/message over a channel 130-G on even numbered hopintervals using scramble code G, relay dismount node 110-3 relays thecommunication/message over a channel 130-I on even numbered hopintervals using scramble code I, relay dismount node 110-4 relays thecommunication/message over a channel 130-B on even numbered hopintervals using scramble code B, relay dismount node 110-5 relays thecommunication/message over a channel 130-D on even numbered hopintervals using scramble code D, relay dismount node 110-6 relays thecommunication/message over a channel 130-E on even numbered hopintervals using scramble code E, and relay dismount node 110-7 relaysthe communication/message over a channel 130-F on even numbered hopintervals using scramble code F.

As will be described in greater detail below, all nodes 110, 120 canperform adaptive space-spectrum whitening (ASSW) via an ASSW module asan effective, robust measure that effectively mitigates interference andjamming. The ASSW technology will be described below with reference toFIG. 6. In addition, each node (e.g., dismount and mounted nodes) cancoherently combine (or beamform) all the received links. For instance,in this example, the mounted node 120 can receive (via a RAKE receiver)at least some of the communications/messages from the sender dismountnode 110-8 and the various relay dismount nodes 110-1 . . . 110-7 andperform beamforming for each hop-code pair. As will also be described ingreater detail below, the mounted node 120 has more antennas and moresignal processing capability than the dismount nodes 110. In oneembodiment, dismount nodes 110 employ two receiver antenna elements andprocess a small subset of all available DSSS signals, whereas themounted node 120 has extra processing capability and supports four ormore antennas. The extra processing capability of the mounted node 120enables it to combine and process DSSS signals received from all of thedismount nodes 110 and to perform adaptive beamforming across fourantennas individually for each link. As such, the multi-beam mountednode 120 can adaptively combine radio (DSSS) signals received from eachdismount node 110 to achieve a distributed cooperative beamformingprocessing gain. Likewise, each dismount node 110 can also adaptivelycombine radio signals received from each node to achieve a distributedcooperative beamforming processing gain.

Downlink Operation: Downlink Communications from Mounted Node toDismount Nodes

During downlink operation of the communication system 100, the mountednode 120 can broadcast downlink communications to each of the dismountnodes 110-1, 110-2, 110-3, 110-4, 110-5, 110-6, 110-7, 110-8 on oddnumbered hop intervals. In other words, the mounted node 120 transmitson odd hops when it is the originator of a network transmission.

In some cases all of the dismount nodes 110 may not receive the downlinkcommunication directly. As such, each dismount node that receives thedownlink communication “error free” can re-broadcast (or relay) thosedownlink communications to the other dismount nodes on even numbered hopintervals. Thus, depending on whether a dismount receives the downlinkcommunication directly from the mounted node 120, or via relay from oneof the other dismount nodes, a particular dismount node could receive onodd numbered hops when downlink communications are directly from themounted node 120, or on even numbered hop intervals for messages relayedfrom other dismount nodes.

To differentiate between these dismount nodes herein, dismount nodes canfall into one of two groups. Dismount nodes can be “relay dismountnodes” when they directly receive downlink communications (on oddnumbered hop intervals) from the mounted node 120, and then relay thosedownlink communications to other dismount nodes (on even numbered hopintervals). By contrast, “listener dismount nodes” refer to dismountnodes that were unable to directly receive error-free downlinkcommunications from the mounted node 120. These listener dismount nodescan receive downlink communications on even numbered hop intervals fromthe relay dismount nodes.

In some scenarios, there are two or more mounted nodes 120 to increaselink robustness and reliability as well as enabling more flexibility innetwork operation by having multiple mounted radios in the formation.When there are two or more mounted nodes 120, the ones of the mountednodes that are not the source or originator of the broadcast message canalso act as relays and rebroadcast the downlink communication on evenhops. When a mounted node 120 operates as a relay (e.g., is not theoriginator of the downlink communication), the mounted node 120transmits or “repeats” any messages, that are received error free, oneven numbered hop intervals.

FIG. 1B illustrates an example of downlink operation of thecommunication system 100 in accordance with the disclosed embodiments.During downlink operation, the mounted node 120 can communicate acommunication/message over a channel 140-H on odd numbered hop intervalsusing a scramble code H. The communication/message from the mounted node120 can be received by one or more of the various dismount nodes 110-1 .. . 110-8. Each of the dismount nodes 110-1 . . . 110-8 that receivesthe code word for the mounted node 120 error free can rebroadcast orretransmit the communication/message on even numbered hop intervals.Dismount nodes process the signal received from the mounted node 120along with any rebroadcasts received from other dismount nodes.

In this non-limiting example shown in FIG. 1B, some of the dismountnodes 110-3 . . . 110-6 function as relay nodes that relay thecommunication/message from the mounted node 120 towards the otherdismount nodes 110-1, 110-2, 110-7, 110-8 using its own unique channelthat is defined by a hop assignment (even numbered hop intervals) and aunique scramble code assigned to the relay dismount node 110-3 . . .110-6. The other dismount nodes 110-1, 110-2, 110-7, 110-8 function aslistener dismount nodes that can receive the communication/message fromone or more of the mounted node 120 and the relay dismount nodes 110-3 .. . 110-6. For example, in this non-limiting example, relay dismountnode 110-3 relays the communication/message from the mounted node 120toward the listener dismount nodes 110-1, 110-2, 110-8 over a channel140-J on even numbered hop intervals using scramble code J. Similarly,relay dismount node 110-4 relays the communication/message from themounted node 120 toward the listener dismount nodes 110-1, 110-2, 110-8over a channel 140-B on even numbered hop intervals using scramble codeB; relay dismount node 110-5 relays the communication/message from themounted node 120 toward the listener dismount nodes 110-2, 110-8, 110-7over a channel 140-D on even numbered hop intervals using scramble codeD; and relay dismount node 110-6 relays the communication/message fromthe mounted node 120 toward the listener dismount nodes 110-1, 110-2,110-7, 110-8 over a channel 140-E on even numbered hop intervals usingscramble code E.

Each of the listener dismount nodes 110-1, 110-2, 110-7 110-8 canpotentially receive (via a RAKE receiver) at least some of thecommunications from the mounted node 120 and one or more of the relaydismount nodes 110-3 . . . 110-6 and perform beamforming across the setof received rebroadcasts from the viable network relay nodes.

Waveform Characteristics

In one embodiment, the nodes 110, 120 communicate using amulti-dimensional FH/DSSS waveform that is robust, jam-resistant, andcontention-free. In one implementation, to help facilitate lowprobability of intercept/low probability of detection (LPI/LPD)signaling, a hybrid FH/DSSS waveform is used, hopping at a hop rate(kilohops/second) and simultaneously spreading at a certain chip rate(megachips/second). As will be described below with reference to FIG. 8,the hop rate and spreading rate of the FH/DSSS waveform can be selectedto depending on the implementation (e.g., up to 10,000 hops/sec (10kilohops/second) and 2.5 megachips/second in one implementation). Thehighest hop rate at sufficient bandwidths can help achieve maximumLPI/LPD and anti-jamming (AJ) performance; however, this comes at thecost of an increased RF signature. On the other hand, lower hop ratescan help achieve optimal LPI/LPD modes that permit reduced RF emissionwith associated improved receiver performance.

As will be described below with reference to FIG. 8, the nodes 110, 120can operate in any frequency band used for commercial radiocommunication. Higher frequencies are preferred due to spectrumavailability, suitability to smaller sized dismount and mounted antenna,and higher propagation loss desirable for LPI/LPD. For example, in oneimplementation, the nodes 110, 120 operate in a portion NATO Band III,1780 MHz to 2680 MHz, which includes the 2.4 GHz ISM band.

The information rates supported by the FH/DSSS waveform can varydepending on the implementation. In one non-limiting implementation, theFH/DSSS waveform supports information rates in the range of 7 kilobytesto 925 kilobytes through flexible Forward Error Correction (FEC) andstructure afforded by DSSS codes. This can support high-qualityPush-to-Talk (PTT) voice, text, and data traffic such as situationalawareness, Position Location Information (PLI), and still images. TheFH/DSSS waveform is scalable such that it can support even higherinformation rates (e.g., information rates required for more bandwidthintensive applications such as full motion video).

To maximize battery life, the FH/DSSS waveform used by the dismountnodes 110 allows “sleeping,” which is contrary to classic militarywaveforms that normally work in continuous receive mode. This can helpreduce the size of the batteries used in the dismount notes 110 and makethem significantly smaller while also allowing the batteries to lastsignificantly longer while also reducing power dissipation, which inturn enables a small form factor to dissipate self-generated heat.

Distributed Beamforming

A combination of technologies enable implementation of distributedbeamforming at the nodes 110, 120. It is desirable to minimize anyexposed RF signature. Employing active beamforming at the nodes 110, 120improves the communications link performance relative to a threatreceiver node. A receiver node is a friendly in-network node, whereas athreat receiver node can be any adversarial electronic warfare (EW)receiver that is not part of the network. To implement distributedbeamforming at the nodes 110, 120, the system 100 can employ aDSSS-based cooperative broadcast, multi-hop network, and adaptivespatial-spectrum whitening (ASSW). Beamforming can be performed withrespect to both the transmit and receive communications. ASSW helpsensure successful signal demodulation when exploiting interference orduring electronic warfare, e.g. jamming.

Each dismount node 110 and each mounted node 120 performs adaptivebeamforming across all viable received node transmissions and theirmulti-path components. As will be explained below, each node includes areceiver that employs a multi-user RAKE (mRAKE) receiver to help improveperformance in dispersive channels and multi-path environments byperforming adaptive, maximal ratio combining (MRC) across the receivedsignals. This approach enables implementing adaptive beamforming foreach received dismount node 110 and their respective multi-pathcomponent. This provides superior results, for example, when the angularspread of the dismounts is large, or when operating in a high multipathenvironment. This approach also permits a single network to havemultiple mounted nodes 120, versus a single mounted node 120,dramatically improving robustness, reliability, and range. Use of CDMApermits space-time combining and reduces complexity. It also enablesoperation at higher frequencies in dispersive channels. In addition, theuse of CDMA as a channel access method permits optimized processing ofeach node's link while maintaining cooperative beamforming gain throughmaximal ratio combining. Furthermore, the use of CDMA as a channelaccess method permits network wide visibility to link status whileenabling adaptive power control and network optimization.

When CDMA is combined with a cooperative broadcast, multi-hop network(discussed below), the link status availability of all nodes is providedvia a synchronization channel (e.g., at half the hop rate) to supportadaptive power control and maintain time synchronization between nodes.To explain further, the synchronization channel sends information tohelp ensure and maintain time synchronization across all network nodes.In addition, the synchronization channel can also communicate linkstatus parameters such as transmit power (e.g., useful for powercontrol). As noted above, the system 100 can employ a transmissionscheme where the originator of a communication communicates on oddnumbered hop intervals, and where the communication is relayed on evennumbered hop intervals (or vice versa). This transmission scheme canprovide the resiliency of “mesh” operation without the complexity. Inother words, the system 100 has a “mesh-like” architecture employingcooperative broadcast, CDMA, multi-hop delivery network to provide theresiliency of mesh and the diversity gains of beamforming, but withoutthe impractical complexity requirements. For example, the cooperativebroadcast, multi-hop network does not require each node to function as arouter, which eliminates the need for routing, monitoring mobilitypatterns of nodes and performing route calculations). In accordance withthe cooperative broadcast, multi-hop network, the dismount node 110originates transmission of a message by broadcasting on odd numbered hopintervals. Other dismount nodes 110 that receive the message error free,can then rebroadcast the message on even numbered hop intervals. Bycontrast, dismount nodes 110, that are not receiving the source node'stransmission error free, can listen to even numbered hop intervals andcombine both signals to retrieve the message. CDMA coding allows areceiver to use different spreading and scrambling codes to separateindividual transmissions of each node. This eliminates the need forcomplex routing algorithms. Each node 110 can broadcast link performancemetrics on a regular basis for the nodes 110 that they are receivingsignals from and processing. This way, link status of the radio networkis propagated to each of the other nodes of the cooperative broadcastmulti-hop network to support adaptive power control required and helpachieve LPD enhancement.

As will be described in greater detail below, the combined FH/DSSSwaveform-network design can provide diversity performance gains acrossthree dimensions: frequency diversity (e.g., through both frequencyhopping and spread-spectrum), time diversity (e.g., leveraged throughcapacity achieving codes and concepts from space-time block coding), andspatial diversity (e.g., benefits and reliability similar tobeamforming, but without the complexity and signaling overhead requiredfor coordination mandated by non-collocated beamforming and combining).

FIG. 2 is an exemplary functional block diagram of a dismount node 110in accordance with the disclosed embodiments. The dismount node 110includes a housing 202 that encloses or houses various hardwarecomponents of the dismount node 110, including an antenna array 210, aRF transceiver 220, a processor unit 230, a Bluetooth/WLAN interface240, a Bluetooth/WLAN antenna 242, memory including a flash memorymodule 250 and a RAM module 260, a battery management system 270, abattery 280, and a wireless charging module 290. The housing 202 alsohas a USB connector 204, an on/off button 206, and a multi-colored LED208. Although not illustrated, the dismount node 110 can also include auser interface (e.g., a microphone, a speaker and optionally a keypad, adisplay or any other element or component that conveys information to auser of the dismount node 110 and/or receives input from the user).

In this embodiment, the antenna array 210 includes a pair of antennas210-1, 210-2 that will be described in greater detail below. It shouldbe appreciated that in other implementations, the dismount node 110 mayalso include additional antennas. The dismount node 110 allows forinter-squad PTT voice and data communications among squad members overshort-range using the FH/DSSS waveform that enables the hardware to bein a low power idle state much of the time to help improve battery life.The dismount node 110 allows for an extended reach-back range to themounted node 120 using cooperative beamforming.

The RF transceiver 220 is electrically coupled to the antenna array 210.The RF transceiver 220 includes a transmitter (not illustrated) and areceiver (not illustrated) to allow transmission and reception of databetween the dismount node 110 and other dismount nodes and the mountednodes 120. In one embodiment, the RF transceiver 220 can be implementedusing an RF Agile transceiver that combines many external RF elementssuch as ADC, DACs, DCXOs, mixers, and amplifier stages into a singlechip. It should be appreciated that in other implementations, thedismount node 110 may also include (not shown) multiple transmitters,multiple receivers, and/or multiple transceivers.

The processor unit 230 controls operation of the dismount node 110. Theprocessor unit 230 may also be referred to as a central processing unit(CPU). The processor unit 230 may comprise or be a component of aprocessing system implemented with one or more processors. The one ormore processors can be implemented with any combination ofgeneral-purpose microprocessors, microcontrollers, digital signalprocessors (DSPs), field programmable gate array (FPGAs), programmablelogic devices (PLDs), controllers, state machines, gated logic, discretehardware components, dedicated hardware finite state machines, or anyother suitable entities that can perform calculations or othermanipulations of information.

In one embodiment, the processor unit 230 includes a processor 232 and aprogrammable logic device 234 (e.g., a flash-based programmable logicdevice) or other electronic components used to build reconfigurabledigital circuits. In one non-limiting embodiment, to help achieve powerand space savings, the processor unit 230 can be implemented using aSystem on Chip (SoC) device that incorporates an ultra-low powermicro-controller and a multi-core applications processor, along with theprogrammable logic device 234 in a compact package. The micro-controlleris responsible for the dismount node's Human-to-Machine (HMI) interface.In one implementation, the micro-controller interfaces to a smartphoneapplication. The micro-controller can detect and quantify the level ofsignals received by the RF transceiver 220. For example, themicrocontroller can detect such signals as total energy, energy persubcarrier per symbol, power spectral density and other signals. In oneimplementation, the micro-controller monitors the RF RSSI. Themulti-core applications processor can perform all upper and physicallayer waveform processing. Each core of the multi-core applicationsprocessor also operates a very low power levels during PTT voice/datamode. Because application processors can efficiently process waveformdata, this reduces the element size of the programmable logic device234, which equates to lower power requirements. In one embodiment, themulti-core applications processor can be implemented using an ARMCortex-A53 processor, and the micro-controller can be implemented usingan ARM M4 core that consumes very low levels of power. The ARMCortex-A53 processor, designed by ARM Holdings, is a low-powersuperscalar processor that implements the ARMv8-A 64-bit instructionset. The programmable logic device 234 provides timing control, aportion of the RF data processing, and physical interfaces between theapplication processor and the RF transceiver 220.

The dismount node 110 can include memory that can provide instructionsand data to the processor unit 230. Memory can include both read-onlymemory (ROM), random access memory (RAM), and non-volatile random accessmemory (NVRAM). In the particular embodiment illustrated in FIG. 2, thememory includes the flash memory module 250 (or other non-volatilecomputer storage medium that can be electrically erased andreprogrammed, while retaining data in the absence of a power supply),and the RAM module 260.

The processor unit 230 typically performs logical and arithmeticoperations based on program instructions stored within the memory. Theinstructions in the memory can be executable to implement the methodsdescribed herein. A computer program product in accordance with anembodiment includes a computer usable storage medium (e.g., memory)having computer-readable program code (e.g., program instructions)embodied therein, wherein the computer-readable program code is adaptedto be executed by one or more processors (e.g., working in connectionwith an operating system) to implement any methods described herein. Inthis regard, the program code (e.g., program instructions) may beimplemented in any desired language, and may be implemented as machinecode, assembly code, byte code, interpretable source code or the like(e.g., via C, C++, Java, Actionscript, Objective-C, Javascript, CSS,XML, and/or others).

The processing unit 230 may also include machine-readable media forstoring software. Software shall be construed broadly to mean any typeof instructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (for example, in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

The Bluetooth/WLAN interface 240 includes at least one Bluetooth modulethat includes one or more WPAN transceivers or Bluetooth transceiversthat are configured to connect node to personal area networks, such as aBluetooth networks. The Bluetooth/WLAN interface 240 includes at leastone WLAN module that includes one or more WLAN transceivers, such asWiFi transceivers, that are configured to connect the node 110 to localarea networks, such as WiFi networks. The Bluetooth/WLAN antenna 242receives Bluetooth and WLAN signals, and transmits Bluetooth and WLANsignals from the node 110. The dismount node 110 can be wirelesslypaired with a smart device (e.g., cellular telephone) via its Bluetoothmodule.

The dismount node 110 has no physical external connectors, using onlywireless interfaces for data, voice, control, and charging. The wirelesscharging module 290 can eliminate the need for external charging. Energyis sent through an inductive coupling to transfer energy throughelectromagnetic induction and charge the battery 280. The battery 280 isa lightweight, high-capacity battery. Battery life depends on manyelements that must work together to limit the use of available energysources. To help optimize battery life, high-capacity batteries 280 areutilized, and the FH/DSSS waveform is designed to keep the activeelements off or idle as much as possible, while hardware is designed toidle at the lowest energy consuming point possible. The batterymanagement system 270 manages the battery 280 by protecting the batteryfrom operating outside its safe operating area, monitoring its state,etc.

FIG. 3A is a block diagram of a software-defined waveform module 300 ofa dismount node 110 in accordance with the disclosed embodiments. Thesoftware-defined waveform module 300 may also be referred to as asoftware-defined hybrid FH/DSSS transceiver module. The software-definedwaveform module 300 includes an antenna array 310, a receiver processingchain 320 that defines a receiver path, a transmitter processing chain340 (also referred to herein as “transmitter”) that defines atransmission path, a media access controller (MAC) module 330, andinput/output (I/O) interface 350. The software-defined waveform module300 is a software-defined radio (SDR) where many of the components thathave been traditionally implemented in hardware (e.g. mixers, filters,amplifiers, modulators/demodulators, detectors, etc.) are implemented bymeans of software on a computer or embedded system. Significant amountsof signal processing are handled by a general-purpose processor, ratherthan being done in special-purpose hardware (electronic circuits). Thesoftware-defined waveform module 300 provides a radio which can receiveand transmit widely different radio protocols (or waveforms) based onthe software used.

Antenna Array

In one non-limiting embodiment, the antenna array 310 includes tworeceive antennas 310-1, 310-2 and one of the antennas 310 serves as atransmit antenna. As noted above, receive operations at the dismountnodes 110 occur on “odd” hop-time intervals. If a code word was notreceived error free, receive operations at the dismount nodes 110 alsooccur on “even” hop-time intervals. As also explained above, the senderdismount node transmits on odd numbered hop intervals, whilere-transmissions by other dismount nodes that receive the sender'stransmission error-free occur on even number hop intervals for floodrouting. Providing two receive antennas 310-1, 310-2 allows forspace-spectrum processing. The antennas 310 also provide a platform toimplement space-time encoding/decoding to improve performance and toperform beamforming on a per link basis by processing DSSS signalsreceived by both two receive antennas 310-1, 310-2 during mRAKE receiver324 processing (as will be described in greater detail below).

Transmitter

The transmitter processing chain 340 includes a broadcast and LDPCencoder module 342, an interleaver module 344, a spreading andscrambling module 346, a modulator module 347, and a beamformer and hopassignment module 348.

Depending on whether the dismount nodes is the original source of atransmission, or acting as a relay node, the broadcast and LDPC encodermodule 342 can receive original information source bits from either theMAC module 330 (when the dismount node is the original source of atransmission) or from the gather, de-interleave and decoder block 328(when the dismount node is acting as a relay node). The broadcast andLDPC encoder module 342 packetizes and encodes the original informationsource bits for each code word with a broadcast or erasure class code(e.g., fountain codes, Luby transform (LT) codes) to ensure reliabletransport, and concatenates a physical layer forward error correction(FEC) code as the inner code to the broadcast code to generate encodedcode words. The type of network or broadcast coding employed can varydepending on the implementation and fall under the general class offountain or erasure codes. These near rateless codes can include, forexample, LT codes, Raptor codes, as well as traditional block codes,e.g. hamming codes. The physical layer's FEC code can include, forexample, convolutional coding, Reed Solomon coding, turbo coding, lowdensity parity check (LDPC) coding. Specifically, in one embodiment, aLDPC ‘short’ code is concatenated with the Bose, Chaudhuri, andHocquenghem (BCH) code or other cyclic error-correcting codes that areconstructed using polynomials over a finite field. As is known in theart, BCH codes form a large class of powerful random error-correctingcyclic codes. In one embodiment, the physical layer FEC code leveragesthe developments of the Digital Video Broadcasting-Second GenerationTerrestrial (DVB-T2) and Digital Video Broadcasting-Satellite-SecondGeneration (DVB-S2) standards. As suggested by theDVB-Next-Generation-Handheld (NGH) standard, the length of the LDPC codecan be made to be used with shorter block sizes (˜4K), motivated bygreater efficiencies and less processing power. Code rates ¼, ½, and ¾can be employed to produce a range of effective bit rates.

Regardless of the implementation, network or broadcast coding helpsensure error-free message distribution by efficiently reconstructingdropped or missing code words from a subset of received packets on theforward link. This method of reliable transport far surpasses thetraditional Automatic Repeat Query (ARQ) protocol's closed-loopresponse, overhead signaling, and increased latency resulting fromre-traversing the network links.

The interleaver module 344 interleaves bits of each encoded code wordacross multiple hops to generate an interleaver output comprisinginterleaved code words for the transmission. The interleaver module 344interleaves a code word across multiple hops to mitigate the degradationdue to loss of a hop due to link or jamming. For example, with a blockinterleaver the code word bits are written row by row into a matrix andthen transmitted column by column. In other embodiments, otherinterleaver approaches can be utilized including, but not limited to,convolutional interleavers, random interleavers, code matchedinterleavers, etc. In one embodiment, the interleaver module 344 can bethe same at each dismount node. In another embodiment, each dismountnode uses a different or unique interleaver so that the loss of a hopdegradation is further minimized. By using a different or uniqueinterleaver module at each of the dismount nodes, performance can beimproved due to the fact each node would have different time-varyingproperties (e.g., symbols from some relayed transmissions might bereceived even if they aren't received from other relayed transmissions).This approach adds more diversity to transmitting dismount nodes sharingcorrelated channels.

The spreading and scrambling module 346 performs a number of differentcoding functions. In one embodiment, each dismount node is assigned adesignated code for scrambling the signal. The codes that are used canvary depending on the implementation. The codes that are used can be anyclass of codes that possess desirable auto and cross correlationproperties (e.g., Kasami and Gold codes). For example, in oneembodiment, each dismount node is assigned a Kasami code for scramblingthe signal over a wide spectrum range. Kasami sequences are binarysequences of length 2N−1 where N is an even integer. Kasami sequenceshave good cross-correlation values. There are two classes of Kasamisequences—the small set and the large set. The spreading and scramblingmodule 346 scrambles the interleaver output signal using the Kasami codeassigned to that dismount node. In one implementation, the protectedFH/DSSS waveform operates at 2.5 megachips/second (Mcps) and up to 10kilohops/second, with a DSSS spreading factor of 32, 16 or 8.

The spreading and scrambling module 346 also uses channelization codesto separate control and data channels. For instance, in one embodiment,the waveform can be spread orthogonal variable spreading factor (OVSF)codes, such as those defined in 3rd Generation Partnership Project(3GPP) specifications. The OVSF codes can be used to provide multiplephysical channels from a single dismount node. In one implementation,the number of OVSF codes per node ranges from two to five. One OVSF codeis dedicated to the pilot sequence for channel tracking, and the otherOVSF codes are used with one, two, or four data channels.

The spreading and scrambling module 346 also employs an AES scramblecode to provide physical layer transmission security (TRANSEC) toprotect transmissions from interception (i.e., to provide lowprobability of interception (LPI)). The AES scramble code also indicatesthe hop number (i.e., time to live (TTL) field). The temporal structureof the AES scramble code provides reliable timing information to deriveframe ordering and also eliminates the overhead required by upper-layersignaling.

Prior to transmission, the spreading and scrambling module 346 cangenerate a spreader output by spreading the interleaver output onto aDSSS signal using the OVSF spreading code to generate a spread signal,and then scramble the spread signal using the both the unique scramblecode assigned to that dismount node together with a common TRANSECscramble code that is shared across the other nodes. The unique scramblecode also identifies that dismount node and can thus be used by othernodes to distinguish transmissions received from that dismount node. Thespreading and scrambling module 346 can also separate control and datachannels using orthogonal variable spreading factor (OVSF) codes toprovide multiple physical channels. Examples of these different physicalchannels can include a pilot channel for tracking, a synchronizationchannel for synchronizing transmissions with those from other dismountnodes so that transmission arrive during a common mRAKE receiver window,and a plurality of data channels. In one embodiment, separate logicalchannels are provided and used for initial synchronization,synchronization maintenance and late joiner synchronization.

In one embodiment, a user or node identifier is determined by itsscramble sequence. For example, in one implementation, the scramble codecan be a Kasami code that is applied after spreading has occurred usinga spreading code, i.e. on a chip basis. This is a unique assignment toeach user node and permits a receiver to distinguish between themultiple transmitting nodes. In addition, a random scramble code (e.g.TRANSEC or AES sequence) can also be applied that is common across allnodes and changes on a per hop basis. As such, this random scramble codeprovides inherent timing information on a hop-by-hop basis. The spreaderoutput from the spreading and scrambling module 346 includes a constant(Kasami) scramble code unique to the node ID and hop-varying TRANSECscramble code. The modulator module 347 (also referred to as modulationmodule 347 or modulator) can modulate the spreader output to generate amodulated output for the transmission. In one embodiment, the modulator347 can convert the chips from the spreading and scrambling module 346into a modulated signal. Examples of modulators that can be used forthis purpose can include, for example, BPSK, QPSK, GMSK, and/or otherfeatureless waveforms. In one embodiment, the modulation module canemploy both BPSK and QPSK modulation to balance receiver sensitivity toachieve bit rates to meet application needs. When combined with the useof one, two, or four OVSF codes this provides a wide range of scalablethroughput each with different LPD detection range performance withoutadding complexity.

The dismount node 110 can also include a beamformer and hop assignmentmodule 348. The hop assignment module (not illustrated) includes aFast-Frequency Hopping (FFH) transmitter that can assign a hop number tofor transmissions by that dismount node to employ fast-frequency hoppingfor LPI. In one embodiment, the hop number is a function of time,whereas hop frequency is based on pseudo-random sequence. A random,non-predictable hop pattern helps achieve LPI. The FH/DSSS waveform canbe designed to tolerate the distortion artifacts (i.e., settling time)associated with rates as high as 10 khop/sec. Optimal LPD performance isachieved at slower hop rates when operating with lower spectralefficiency (or more coding gain). The beamformer module (notillustrated) can update amplitude and phase weightings of the DSSSsignal that is provided to the two or more antennas. Notably, dismountnodes perform receive beamforming and generally do not perform transmitbeamforming due to their broadcast nature. However, in someimplementations, there is nothing precluding a dismount node from doingtransmit beamforming if the situation warrants. By contrast, mountednodes can perform receive beamforming, and also perform transmitbeamforming for reach back to a squad. The transmit beamforming is basedon channel reciprocity.

Receiver

The receiver processing chain 320 includes a de-hop and the adaptivespace-spectrum whitener 322, a multi-user RAKE receiver 324, a maximumlikelihood ratio combiner module 326, a data de-spreader module 327, anda gather, de-interleave and decoder block 328. In comparison toconventional cooperative broadcast receivers, the receiver 320 avoidsthe need of excessive coordination and multi-user detection, and is alsosignificantly less complex, requires less processing, more economical,and approaches similar diversity gains typically only afforded to beamcombining. As will be explained in greater detail below, the receivedsignal(s) from multiple transmitters (e.g., one or more transmitters)will be the combined by the receiver 320. Joint demodulation can beperformed by using information spanning multiple consecutive hops. Byusing information across multiple hops spanning more time, more channelinformation can be utilized. The cooperative beam combining strategyhelps ensure that diversity is maintained by reducing or minimizingdestructive interference. When applying this strategy encoded over amodern FEC block code, diversity gains approaching beam combining can beachieved with far lower complexity and cost.

The de-hop and the adaptive space-spectrum whitener 322 channelizes theinput spectrum and the adaptive space-spectrum whitener uses covarianceanalysis to detect and remove large interference from the receivedsignal to provide jammer/interference mitigation. The use of two receiveantennas 310-1, 310-2 allows one interferer/jammer to be removed fromeach channel. To explain further, in one embodiment, the de-hop and theadaptive space-spectrum whitener 322 can include a de-hop module and anadaptive space-spectrum whitener module. The de-hop module can de-hopeach of the received DSSS signals by tuning to a particular frequency toreceive each DSSS signal and then channelizes the input spectrum foreach of the received DSSS signals to generate beam samples for each ofthe channelized signals. The adaptive space-spectrum whitener module canperform adaptive space-spectrum whitening to detect and removeinterference signals from each channel by performing a covarianceanalysis to generate channelized versions of the DSSS signals. Eachchannelized version of DSSS signals comprises transformed beam samplesfor each channel.

In this embodiment, the multi-user RAKE receiver 324 and the maximumlikelihood ratio combiner module 326 collectively provide amulti-channel beamformer module that can perform cooperative beamformingon a per channel (or per link) basis by processing signals received byboth two receive antennas 310-1, 310-2 (with interference removed) andcoherently combining a subset of transmissions and multipath componentsfor each transmission that are received from other nodes together andhave sufficient signal strength (e.g., greater than or equal to athreshold) to be beneficial to the coherent combining. In oneembodiment, this can be accomplished by time aligning the respectivesignals of interest, and removing frequency offset and phase offset fromeach transmission. The number of transmissions in the subset can beselected, for example, based on processing power, battery life andperformance. This can include downlink transmissions received from theother nodes including: (1) any downlink transmission that is receivederror free from the mounted node, and multi-path components of anydownlink transmission that is received error free from the mounted node;and (2) any re-transmitted downlink transmissions that are receivederror free from relay dismount nodes, and any multi-path components ofany re-transmitted downlink transmissions that are received error freefrom relay dismount nodes.

To explain further, in one embodiment, the multi-user RAKE receiver 324processes each of the channelized signals (e.g., signals received byboth two receive antennas 310-1, 310-2 with interference mitigated)during mRAKE receiver 324 demodulation processing. In one embodiment,the multi-user RAKE receiver 324 performs RAKE receiver demodulationprocessing aided by the scramble codes and OVSF separated pilot signal.Scramble code correlations can be performed on a per channel basis toalign symbols of each of the channelized signals (e.g., perform symbolalignment without the overhead of framing or field counters). Oneexample implementation of the multi-user RAKE receiver 324 will bedescribed in greater detail below with reference to FIG. 3B.

The use of DSSS coding allows the receiver to maximally ratio combine(or combined beamform) the signals received from radios of multipletransmitting nodes. This approach allows for operation in severe delaydispersive environments (e.g., forest and urban) and with fast movingmobile users. Once the soft decisions are received across all scramblecodes, the maximum likelihood ratio combiner module 326 maximally ratiocombines (or combine beamforms) aligned symbols for each of output fromeach of the number (N) of fingers, on a per channel basis, to generate asoft decision across each of the multiple channels, and then combinesthe soft decisions into a joint soft decision for use by the datade-spreader module 327, and then the gather, de-interleave and decoderblock 328 during forward error correction (FEC) and broadcast decoding(described below).

The data de-spreader module 327 converts the chips from the combinedsignal to data symbols. In other words, the data despreader module 327despreads chips to generate data symbols that can then be provided tothe gather, de-interleave and decoder block 328.

The gather, de-interleave and decoder block 328 gathers data acrossmultiple hops to form soft-decision codeword bits, which can be referredto as log-likelihood ratio (LLRs). The gather, de-interleave and decoderblock 328 can include a gather block that concatenates the datasoft-decision bits from each hop across multiple received hops togetherto form codeword soft-decision bits, a de-interleaver block that cande-interleave the codeword soft-decision bits, and a decoder block thatcan perform low density parity check (LDPC) forward error correction(FEC) decoding and broadcast decoding on the codeword soft-decision bitsto recover information bits corresponding to the complete codeword. Asnoted above, the types of coding used in the network can vary dependingon the implementation and can include LT codes, Raptor codes, fountaincodes for broadcast erasure type code, and convolutional coding, ReedSolomon coding, turbo coding, low density parity check (LDPC) coding forphysical layer forward error correction (FEC). In one implementation, a4096 symbol LDPC decoder is used with rates of ¼, ½ and ¾. For QPSKmodulation, each I/Q rail is processed as a separate code word. In oneimplementation, multiple I-Q channels are dedicated to the samecodeword. When utilizing multiple OVSF codes for more data channels, upto eight (8) code words are processed. To minimize the processing impactof multiple FEC channels, higher rates only utilize higher coding rates.QPSK uses rate 1/2 and ¾ codes, whereas multiple OVSF are QPSK and rate3/4 only. Adding further resiliency, an outer broadcast code brings thecapability to reconstruct missing or dropped information packets.

In one embodiment, the MAC module 330 can include a power control modulethat encodes power control information (e.g., transmit power) in a PTTpacket. The power control module (not shown) can add link statusinformation to the packet and propagate link status information throughthe network through short link status messages. This permits nodes toperform “what if” scenarios to determine the effect of either increasingor reducing the power when sending or relaying a message. To explainfurther, a source node (that originates the transmission) can encode themessage with its transmit power. As noted above, the source nodetransmits on odd numbered hop intervals. Nodes that receive the messagecan estimate the receive SNR, and together with knowledge of the sourcenode's transmit power, can adjust their transmit power and re-transmitrelevant messaging including their transmit power on even numbered hopintervals. The source node and other relay nodes will receive thatmessage, estimate SNR, and re-adjust their transmit power. In oneembodiment, this information can be encoded in both synchronizationmessages and push-to-talk (PTT) messages. Given the dynamic nature ofdismount nodes in terrain, and the broadcast relay approach, this willbe a slow loop (seconds) that is based upon adjusting link margin toterrain-environment (e.g., versus a cellular approach to adjust transmitpower to instantaneous conditions at rates of 1500 Hz).

When the dismount node is a source/sender that is transmitting data fromthe physical layer, the input/output (I/O) interface 350 provides datato the MAC module 330, and the MAC module 330 serves as the data bitsource. For example, the MAC module 330 encapsulates higher-level framesinto frames appropriate for the transmission medium (e.g., the MAC addsa syncword preamble and also padding if necessary), adds a frame checksequence to identify transmission errors, and then forwards the data tothe physical layer as soon as the appropriate channel access methodpermits it. The MAC module 330 controls when data is sent and when towait to avoid congestion and collisions. The MAC module 330 is alsoresponsible for initiating retransmission if a jam signal is detected,and/or negotiating a slower transmission rate if necessary.

When receiving data from the gather, de-interleave and decoder block328, the MAC module 330 ensures data integrity by verifying the sender'sframe check sequences, strips off the sender's preamble and padding,before passing the data up to the higher layers where code wordsreceived from the gather, de-interleave and decoder block 328 aretranslated into actual data (e.g., voice packets, IP packets, Ethernetframes, or any other type of I/O, etc.) and eventually to theinput/output (I/O) interface 350.

Due to reflections from obstacles a radio channel can consist of manycopies of originally transmitted signals having different amplitudes,phases, and delays. Multipath components are delayed copies of theoriginal transmitted wave traveling through a different echo path, eachwith a different magnitude and time-of-arrival at the receiver. In otherwords, the multipath components are time-delayed versions of theoriginal signal transmission. Since each component contains the originalinformation, if the magnitude and time-of-arrival (phase) of eachcomponent is computed at the receiver, the multipath components can becombined to improve information reliability.

FIG. 3B shows a block diagram of a portion of the receiver processingchain 320 of FIG. 3A in accordance with one implementation of thedisclosed embodiments. In particular, FIG. 3B illustrates the antennas310-1, 310-2 and corresponding RRC matched filters 311-1, 311-2, themulti-user RAKE (mRAKE) receiver 324 of FIG. 3A in one particularimplementation, a maximum likelihood ratio combiner module 326, a datadespreader module 327, and a gather, de-interleave and decoder block328.

As shown in FIG. 3B, each antenna 310 receives incoming signals on theirrespective spatial channel which is then sent to a corresponding RRCmatched filter 311. Each receive antenna channel can includetransmissions that are directly received from one or more nodes, and/orone or more multipath components of those transmissions. As such, thesignals received by each antenna can include signals that are receiveddirectly from one or more the nodes, and/or multipath components ofthose signals. Each RRC matched filter 311 then filters the incomingsignals to isolate the frequency spectrum containing the signal ofinterest, and generates outputs that are then provided to an adaptivespace-spectrum whitener 322-1, which can be one part of the de-hop andthe adaptive space-spectrum whitener 322 of FIG. 3A.

The adaptive space-spectrum whitener 322-1 can perform adaptivespace-spectrum whitening to detect and remove interference signals fromeach channel by performing a covariance analysis to generate channelizedversions of the DSSS signals. Each channelized version of DSSS signalscomprises transformed beam samples for each channel. The adaptivespace-spectrum whitener 322-1 outputs channelized signals (received byboth the receive antennas 310-1, 310-2 with the interference mitigated)to the correlation modules 361-1 and 361-2 of the mRAKE receiver 324.

A conventional RAKE receiver combines multipath components of a singlereceived transmission. By contrast, the multi-user RAKE or mRAKEreceiver 324 in accordance with the disclosed embodiments combines nodetransmissions and multipath receptions of multiple received nodetransmissions. Thus, instead of multiple RAKE receivers assigned tomultiple users, the mRAKE receiver 324 receiver correlates over multipleusers, frequencies and their respective multipath component(s). Themulti-user RAKE receiver 324 includes correlation modules 361-1 and361-2 and a finger selection module 362. Each of the correlation modules361-1, 361-2 includes correlator banks for each node 1, . . . , N.

As noted above, the adaptive space-spectrum whitener 322-1 outputs twowhitened spatial streams to the respective correlation modules 361-1 and361-2. Each whitened spatial stream is a linear combination of theoriginal spatial stream resulting from the antennas 310-1 and 310-2. Oneor more of these spatial whitened streams will contain the signal ofinterest with the interference mitigated. As such, each correlationmodule 361 (also referred to as correlator banks 361) can process onespatial stream that is output from the adaptive space-spectrum whitener322-1.

As shown in FIG. 3B, each correlator module 361 includes one correlatorblock for each of the N nodes. Each correlator block performscorrelation for a particular node by processing a spatial streamreceived from the adaptive space-spectrum whitener 322-1 and acorresponding scramble code for a particular node. In other words, eachcorrelator block is driven by a unique scramble code that identifiestransmissions from a particular node (and that can be used todistinguish transmissions received from that particular node from thosereceived from other nodes). Each correlator block can receive signalsthat can include transmissions from any number of nodes and/ormulti-path components of those transmissions, and determinechannel-multipath correlations. Based on a received signal and one ofthe scramble codes, each correlator can generate one or more mRAKEfingers. Each finger corresponds to a specific channel. Each finger canbe, for example, a specific channel/signal pair for a particular node,or a specific channel/multipath component pair for a particular node. Inthis particular non-limiting example shown in FIG. 3B, the correspondingscramble code that is input to each correlator block is a Kasami codefor a particular node that is logically combined (e.g., XOR-ed) with asecurity code (e.g., a TRANSEC code). Each correlator block processesthe outputs from the adaptive space-spectrum whitener 322-1 and itscorresponding scramble code to determine the mRAKE's candidate fingers'multipath location and respective complex weight

The fingers from each correlator block are input to the finger selectionmodule 362. The finger selection module 362 selects a subset (F) ofthese fingers that have sufficient correlation and outputs one or moreof the fingers (F). The finger selection module 362 selects which nodescontribute to the F total largest signal multipath components received.

The maximum likelihood ratio combiner module 326 includes a plurality (1. . . N) of processing modules 363 and a coherent combiner module 368.Each of the processing modules 363 include a coherent combiner module364-1 . . . 364-N, a descrambler 365-1 . . . 365-N, and a pilotdespreader module 367-1 . . . 367-N. Each processing module 363corresponds to a particular node (N1 . . . NN) of the network andprocesses signals for that node (N1 . . . NN), where N is less than orequal to F. Each processing module 363 includes a coherent combinemodule 364, a descrambler 365, and pilot despreader module 367.

In this embodiment, the finger selection module 362 outputs a number ofthe subset of fingers 1 . . . F to a corresponding coherent combinemodule 364-1 . . . 364-N of each processing module 363-1 . . . 363-N.Each coherent combine module 364 receives a number of fingers (labeledas Finger 1 through Finger K) and coherently combines the fingers(labeled as Finger 1 through Finger K) to generate an output signal thatis then processed by a corresponding descrambler 365. As such, one ormore of the fingers (1 . . . K1) are input to a coherent combine module364-1 for Node 1, one or more of the fingers (K1+1 . . . K2) are inputto a coherent combine module 364-2 for Node 2, . . . one or more of thefingers (F-KN+1 . . . F) are input to a coherent combine module 364-Nfor Node N, where N<=F. The output of each coherent combine module 364-1. . . 364-N for each node is sent to a corresponding descrambler 365-1 .. . 365-N. As such, the output of the coherent combine module 364-1 forNode 1 is provided to descrambler 365-1, the output of coherent combinemodule 364-2 for Node 2 is provided to descrambler 365-2, . . . and theoutput of the coherent combine module 364-N for Node N is provided todescrambler 365-N.

In one embodiment, each descrambler 365 processes one or more of thefingers output by its corresponding coherent combine module 364 using acode (e.g., Kasami code for a particular node, AES code and/orcombination of a Kasami code and an AES code) to descramble the outputof its corresponding coherent combine module 364. A descrambled signaloutput by each descrambler 365 is then provided to a corresponding pilotdespreader module 367, which can process the descrambled signal that itreceives to generate a despread pilot signal. As will be explainedbelow, the despread pilot signals are used by the coherent combinermodule 368 to coherently combine the descrambled signals that are outputfrom each of the descramblers 365-1 . . . 365-N. The resulting despreadpilot signals for each received node can permit more accurate timing andphase tracking to maximize the coherent combining of the descrambledsignals received across multiple nodes.

The coherent combiner module 368 coherently combines descrambled signalsthat are output from each of the descramblers 365-1 . . . 365-N of theprocessing modules 363-1 . . . 363-N. To explain further, each of thedescrambled signals from the descrambler modules 365-1 . . . 365-N (showas solid lines in FIG. 3B) can then be coherently combined at thecoherent combiner module 368. The coherent combiner module 368 can beimplemented as one part of the maximum likelihood ratio combiner module326 of FIG. 3A. In other words, each of the descrambled signals (outputby the Kasami/AES descrambler modules 365-1 . . . 365-N) can then becoherently combined (at the coherent combiner module 368) across alluser nodes to generate a coherently constructed signal. To explainfurther, in one embodiment, the coherent combiner module 368 coherentlycombines, using pilot soft-decision bits from each of the despread pilotsignals for each node, each of the descrambled signals received acrossmultiple nodes to generate a coherently constructed signal of spreaddata channels that includes a coherently combined vector of chips ofinformation, which is then provided to the data despreader module 327.

Maximal-ratio combining is a form of diversity combining that yields themaximal SNR achievable. It requires the exact knowledge of SNRs as wellas the phases of the diversity signals. The symbols from allocatedfingers can be maximal-ratio-combined to construct a coherently“combined” symbol. For example, the output symbols from differentfingers are multiplied with complex conjugate of the channel estimateand the result of multiplication is summed together into the “combined”symbol. If maximal-ratio combining is implemented, the overall decisionstatistic (Z′) can be expressed in equation (1) as follows:

$\begin{matrix}{{Z^{\text{?}} = {\sum\limits_{\text{?}}^{M}\text{?}}}{\text{?}\text{indicates text missing or illegible when filed}}} & (1)\end{matrix}$

The weighting coefficients, am, represent finger weights, and, in oneimplementation, can be normalized to the output signal power of thecorrelator in such a way that the coefficients sum to unity.

Referring again to FIG. 3B, the data despreader module 327 converts thechips from the respective data channels to generate demodulated datasymbols that are converted into data soft-decision bits that can then beprovided to the gather, de-interleave and decoder block 328. The gather,de-interleave and decoder block can include a gather block thatconcatenates the data soft-decision bits from each hop across multiplereceived hops together to form codeword soft-decision bits, ade-interleaver block that can de-interleave the codeword soft-decisionbits, and a decoder block that can perform low density parity check(LDPC) forward error correction (FEC) decoding and broadcast decoding onthe codeword soft-decision bits to recover information bitscorresponding to the complete codeword. For example, in oneimplementation, during transmission, the FEC codeword produced by thebroadcast and LDPC encoder module 342 is transmitted through beamformerand hop assignment module 348 spanning multiple hops enhancingdiversity. At the receiver, the gather, de-interleave and decoder block328 concatenates the demodulated data symbols across multiple receivedhops accumulating data symbols or data soft-decision bits correspondingto a complete codeword. The data soft decision bits are thende-interleaved via a de-interleaver of the gather, de-interleave anddecoder block 328. The gather, de-interleave and decoder block 328decodes the symbols to generate information bits that are then providedto the MAC module 330 of FIG. 3A

FIG. 4 is an exemplary functional block diagram of a mounted node 120 inaccordance with the disclosed embodiments. The mounted node 120 includesa housing (not shown) that encloses or houses various hardwarecomponents of the mounted node 120. Hardware components of the mountednode 120 can include at least one multi-band antenna array 410-1 (andoptionally additional multi-band antenna arrays 410-2 . . . 410-4), anda computer platform 420. The computer platform 420 includes an RFtransceiver 430, an Ethernet switch 440, a processor unit 450, memory460, and a power supply 480 that receives vehicle power 490 used topower the mounted node 120. Although not illustrated, the mounted node120 can include a user interface (e.g., a microphone, a speaker andoptionally a keypad, a display or any other element or component thatconveys information to a user of the mounted node 120 and/or receivesinput from the user).

In this embodiment, each antenna array 410 includes four or moreantennas (not illustrated in FIG. 4) as will be described in greaterdetail below with reference to FIG. 5. It should be appreciated that inother implementations, the mounted node 120 may also include additionalantenna arrays 410-2 . . . 410-4. The mounted node 120 allows for voiceand data communications with squad members using the FH/DSSS waveformand cooperative beamforming.

The mounted node 120 also includes RF front end 425 which synchronouslydigitizes the receive signals from each antenna as well as transmits thewaveform. Each antenna represents a single channel. In one embodiment,the mounted can have multiple channels. The RF transceiver 430 iselectrically coupled to the antenna array(s) 410. The RF transceiver 430includes a transmitter (not illustrated in FIG. 4) and a receiver (notillustrated in FIG. 4) to allow transmission of data to, and receptionof data from, other dismount nodes and the mounted node 120 (andoptionally other mounted nodes that are not illustrated in FIG. 1). Assuch, the RF transceiver 430 receives communications from the variousnodes, and transmits communications to the various nodes. It should beappreciated that in other implementations, the mounted node 120 may alsoinclude (not shown) multiple transmitters, multiple receivers, and/ormultiple transceivers.

The Ethernet switch 440 can support IP connectivity for mobilecommunications, and includes multiple Ethernet ports to support multipleantennas. The processor unit 450 controls operation of the mounted node120. The processor unit 450 may also be referred to as a centralprocessing unit (CPU). The processor unit 450 may comprise or be acomponent of a processing system implemented with one or moreprocessors. The one or more processors can be implemented with anycombination of general-purpose microprocessors, microcontrollers,digital signal processors (DSPs), field programmable gate array (FPGAs),programmable logic devices (PLDs), controllers, state machines, gatedlogic, discrete hardware components, dedicated hardware finite statemachines, or any other suitable entities that can perform calculationsor other manipulations of information. The processor unit 450 performsnumerous functions for the mounted noted. For example, the processorunit 450 controls a Human-to-Machine (HMI) interface (not illustrated inFIG. 4), interfaces with the RF transceiver 430, performs RF dataprocessing, detects and quantifies the level of signals received by theRF transceiver 430, performs all upper and physical layer waveformprocessing, provides timing control, etc.

The memory 460 can provide instructions and data to the processor unit450. The processor unit 450 typically performs logical and arithmeticoperations based on program instructions stored within the memory. Theinstructions in the memory can be executable to implement the methodsdescribed herein. Memory can include both read-only memory (ROM), randomaccess memory (RAM), and non-volatile random access memory (NVRAM). Theprocessor unit 450 may also include machine-readable media for storingsoftware. Software shall be construed broadly to mean any type ofinstructions, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise. Instructions mayinclude code (for example, in source code format, binary code format,executable code format, or any other suitable format of code). Theinstructions, when executed by the one or more processors, cause theprocessing system to perform the various functions described herein.

In one embodiment, the power supply 480 can be a power supply designedto meet the MIL-STD-1275E standard requirements are typically used inmilitary ground vehicle power applications that employ a nominal 28 Vpower supply system that is able to handle transient spikes and surges.

FIG. 5 is a block diagram of a software-defined waveform module 500 of amounted node 120 in accordance with the disclosed embodiments. Thesoftware-defined waveform module 500 may also be referred to as asoftware-defined hybrid FH/DSSS transceiver module. As noted above, themounted node 120 transmits on odd numbered hop intervals when it is theoriginator of a network transmission. By contrast, the mounted node 120transmits on even hops when it operates as a relay (e.g., is not theoriginator) and repeats (i.e., re-transmits) the received messages whenthey have been received error free.

The software-defined waveform module 500 includes an antenna array 510,a receiver processing chain 520 that defines a receiver path, atransmitter processing chain 540 (also referred to herein as“transmitter”) that defines a transmission path, a media accesscontroller 530, and an input/output (I/O) interface 550. As shown inFIG. 5, the software-defined waveform module 500 includes many of thesame blocks as the dismount node 110 that were described above withreference to FIG. 3A, and the processing performed by similar blocks isessentially the same. For sake of brevity, the description of blocksthat are the same or similar to those in FIG. 3A will not be repeatedagain with reference to FIG. 5. The main differences between thesoftware-defined waveform module 500 of the mounted node 120, and thesoftware-defined waveform module 300 of the dismount node 110 (shown inFIG. 3A) will now be described below.

Antenna Array

Because the mounted node 120 does not have the same size and powerconstraints as a dismount node, the mounted node 120 can have moreantennas 510-1 . . . 510-4 and additional processing resources. In onenon-limiting embodiment, each antenna array 510 includes four receiveand transmit antennas 510-1, 510-2, 510-3, 510-4. The antennas 510-1,510-2, 510-3, 510-4 of the mounted node are part of a multi-band phasedantenna array having a number (N) of antennas that including at leastthe first, second, third and fourth antennas 510-1, 510-2, 510-3, 510-4.Each antenna 510-1, 510-2, 510-3, 510-4 of the multi-band phased antennaarray is configured to receive DSSS signals from one or more dismountnodes and generate an output.

Transmitter

The transmitter processing chain 540 includes a broadcast and LDPCencoder module 542, an interleaver module 544, a spreading andscrambling module 546, a modulator 547 and a beamformer and hopassignment module 548. The broadcast and LDPC encoder module 542,interleaver module 544 and the spreading and scrambling module 546 alsooperate similar to corresponding elements of the dismount node 110 thatare described above with reference to FIG. 3A and therefore thedescription of those elements will not be repeated for sake of brevity.

The mounted node 120 can also include a beamformer and hop assignmentmodule 548. As with the beamformer and hop assignment module 348, thehop assignment module (not illustrated) includes a Fast-FrequencyHopping (FFH) transmitter that can assign a hop number to fortransmissions by that mounted node to employ fast-frequency hopping forLPI. In one embodiment, the frequency-to-hop interval mapping can bedefined by an encryption sequence (e.g. Advanced Encryption Standard(AES) key stream). The AES, also known by its original name Rijndael, isa specification for the encryption of electronic data established by theU.S. National Institute of Standards and Technology (NIST) in 2001. Thealgorithm described by AES is a symmetric-key algorithm, meaning thesame key is used for both encrypting and decrypting the data. However,the beamformer module of the beamformer and hop assignment module 548 ofthe mounted node 120 differs from the beamformer and hop assignmentmodule 348 of the dismount node 110. The beamformer and hop assignmentmodule 548 of the mounted node 120 implements transmit beamforming tofocus RF emissions towards the dismount nodes 110 of the network. Theformed beams are formed based upon the receiver beamforming information.In high mobility scenarios the initial beam will be broad, and uponreceiving relay dismount nodes 110 retransmissions on even hops thebeams will be dynamically updated to focus transmissions towards thoserelay dismount nodes 110, while reducing RF power in other directions.

Receiver

As will be explained in greater detail below, the receiver 520 combinesreceived signal(s) from one or more of the dismount nodes 110 using acooperative beam combining strategy that helps ensure that diversity ismaintained by minimizing destructive interference. When applying thisstrategy encoded over a modern FEC block code, diversity gainsapproaching ideal transmit beam combining can be achieved. To explainfurther, in comparison to conventional distributed cooperative broadcastbeamforming, the choice to beamform at receiver 520 avoids the need ofexcessive coordination, is significantly less complex, scalable,operates over extensive channels and frequency bands, requires lessprocessing, more economical, and approaches similar diversity gainstypically only afforded to transmit beam forming with far lowercomplexity and cost.

Referring again to FIG. 5, the receiver processing chain 520 includes ade-hop and adaptive space-spectrum whitener 522, a multi-channelbeamformer module 523, a multi-user RAKE receiver 524, a maximumlikelihood ratio combiner module 526, a data despreader module 527, anda gather, de-interleave and decoder block 528. As explained above,receive operations at the mounted node 120 occur on odd numbered hopintervals. If a code word was not received error free, receiveoperations at the mounted node 120 also occur on even numbered hopintervals. Processing performed by the receiver processing chain 520 ofthe mounted node 120 is similar to that performed by the dismount radiowith some differences that will now be described.

The de-hop and the adaptive space-spectrum whitener 522 operates similarto corresponding elements of the dismount node 110 that are describedabove with reference to FIG. 3A, and therefore the description of thosemodules will not be repeated here with respect to FIG. 5 for sake ofbrevity. A difference is that performance is improved through the use ofadditional antennas 510, and as such, the de-hop and the adaptivespace-spectrum whitener 522 processes more input information (e.g., fourinputs from four receive antennas versus two antennas in FIG. 3A) andgenerates more output information (e.g., four outputs versus two outputsin FIG. 3A). Although the embodiment illustrated in FIG. 5 includes fourantennas, it should be appreciated that other numbers of antennas can beimplemented depending on the implementation. With the additional spatialchannels and spatial streams of output information from thespace-spectrum whitener 522, the multi-channel beamformer 523 andmulti-user RAKE 524 are capable of producing higher receive signal SNRafforded by both the mounted unit's additional channels and processingcapability.

The use of four receive antennas 510-1, 510-2, 510-3, 510-4 allows themounted node 120 to extend and enhance the signal processingcapabilities of the mounted node 120, and also allow for enhancedcooperative beamforming capabilities via a multi-channel beamformermodule 523 (that will be described below). Significant performancedifferences include: active transmit and receive beamforming across fourantenna 510-1 . . . 510-4 and more capable space-spectrumjammer/interference mitigation, and the processing of more RAKE fingers(at multi-user RAKE receiver 524) combining more nodes into the uplinkbeamforming. At a simplistic level, the additional processing providesrange extension to the squad network without increasing the RF signatureof the squad thereby helping to maintain the LPD capability of thesquad.

The multi-channel beamformer module 523 performs beamforming on a perlink/channel basis by processing signals received by the receiveantennas 510-1, 510-2, 510-3, 510-4 with interference removed. Toexplain further, the multi-channel beamformer module 523 can performbeamforming on a per channel basis by coherently combining all of theDSS signals received from the dismount nodes by performing a matrixoperation that linearly transforms the channelized signals (e.g.,outputs received from each of the number (N) of antennas) into a smallernumber (NT) of directional beams. As such, the transmissions receivedacross each of the number (N) of antennas of the multi-band antennaarray can be coherently combined on a per link basis to generate acorresponding directional beam. For example, the multi-channelbeamformer module 523 can perform a matrix operation that transformsinputs from N (e.g., 4) antennas of the phased array antenna into anumber (NT) of received beams (like sectors) to improve SNR, while alsopotentially reducing the number of channels that need to be processed(e.g., 16 antennas, but only 4 beams are ultimately fed into themulti-user RAKE receiver 524).

In one embodiment, to provide adaptive beamforming received from eachtransmitting node (sender and/or relay), the multi-channel beamformermodule 523 performs a linear transformation of the whitened spatialstreams to create multiple directional beams. Each directional beamcovers a portion of the azimuth range. Multiple sectors are thenadaptively combined for each received link. This sectorization isprovides sufficient carrier-to-noise ratio (C/N) for the multi-user RAKEreceiver 524 based “fine-tuned” beamforming and further supportsoperation on-the-move.

The multi-user RAKE (mRAKE) receiver 524 can process each of thedirectional beams output by the multi-channel beamformer module 523 andalign symbols using scramble code correlation. This is because themounted node 120 has significantly more processing capability than thedismount nodes, which allows more RAKE fingers to be processed by themounted node 120 (compared to the dismount node). During RAKE receiver524 processing, the multi-user RAKE receiver 524 processes signalsreceived by the receive antennas 510-1, 510-2, 510-3, 510-4 withinterference removed. In one embodiment, the multi-user RAKE receiver524 performs RAKE receiver demodulation processing across multiple usersaided by the OVSF separated pilot signal. Scramble code correlation isused to align symbols (e.g., perform symbol alignment without theoverhead of framing or field counters).

The maximum likelihood ratio combiner module 526, the data despreadermodule 327, the gather, de-interleave and decoder block 528, the MACmodule 530, and the input/output (I/O) interface 550 each operatesimilar to the corresponding elements of the dismount node 110 that aredescribed above with reference to FIG. 3A. As such, the description ofthose modules will not be repeated here with respect to FIG. 5 for sakeof brevity. Signal processing operation is enhanced due to additionalcomputational resources afforded by the mounted unit.

FIG. 6 is a block diagram 600 that illustrates one non-limitingimplementation of an adaptive space-spectrum whitener 522′ that is partof the de-hop and the adaptive space-spectrum whitener 522 of FIG. 5 inaccordance with the disclosed embodiments. Although the adaptivespace-spectrum whitener 522′ of FIG. 5 is implemented at the mountednode 120, it should be appreciated that the same adaptive space-spectrumwhitener can be implemented within the de-hop and the adaptivespace-spectrum whitener 322 of FIG. 3A. The number of antennas definesthe spatial dimensionality and impacts the degrees of freedom. Theincrease in dimensionality permits an increase in effectiveness incertain scenarios.

The antenna array 510 (that includes antennas 510-1 . . . 510-4) isdescribed above with reference to FIG. 5 and therefore the descriptionof the antenna array 510 will not be repeated here with reference toFIG. 6. The adaptive space-spectrum whitener 522′ is an interferencemitigation module that includes a modified Discrete Fourier Transform(MDFT) analysis module that includes an MDFT analysis bank 620-1 . . .620-4 corresponding to each antenna 510-1 . . . 510-4, an adaptiveinterference mitigation space-frequency whitener module 640, and a MDFTsynthesis module that includes a MDFT synthesis bank 660-1 . . . 660-4for each beam 650-1 . . . 650-4.

Each MDFT analysis bank 620-1 . . . 620-4 can receive a beam (e.g., adigitized spatial stream of frequency channelized RF samples) from acorresponding antenna 510-1 . . . 510-4. The RF samples from each of thefour beams are digitized to preserve spatial diversity. Each MDFTanalysis bank 620-1 . . . 620-4 can channelize the beam (e.g., digitizedspatial stream) it receives in the spectral domain to generate afrequency channelized beam of samples 630-1 . . . 630-4 (also referredto herein as a channelized beam) to enable perfect (or near perfect)reconstruction.

Each channelized beam 630-1 . . . 630-4 generated by one of the MDFTanalysis bank 620-1 . . . 620-4 includes multiple (e.g., 32) spectralchannels. Together, the channelized beams 630-1 . . . 630-4 include anumber of spectral-spatial channels. For example, in this non-limitingembodiment, where there are four MDFT analysis banks 620-1 . . . 620-4(and hence four channelized beams 630-1 . . . 630-4) and 32 spectralchannels per MDFT analysis bank 620-1 . . . 620-4, there would be 128spectral-spatial channels (4 spatial by 32 spectral). Collectively, thechannelized beams 630-1 . . . 630-4 form a spatial-spectral matrix (Z),where each row of the matrix represents spatial-spectral samples uniqueto its respective channelized beam, and where each column of thespatial-spectral matrix (Z) represents time indices. Stated differently,the spatial-spectral matrix (Z) is a matrix of time-frequency samplesacross the multiple antennas (i.e., the channelized spatial-spectralsamples 630-1 . . . 630-4 from each MDFT analysis bank 620-1 . . .620-4).

The adaptive interference mitigation space-frequency whitener module 640receives the spatial-spectral matrix (Z), and applies a whitening matrix(W) to the spatial-spectral matrix (Z) to remove interference andpreserve the signal of interest. Stated differently, the adaptiveinterference mitigation space-frequency whitener module 640 calculatesthe auto-correlation matrices across the relevant rows of matrix (Z)such that the resulting correlation matrix is white (diagonal matrix).As such, the adaptive interference mitigation space-frequency whitenermodule 640 can generate a whitened matrix (WZ) 650 that includesinterference-mitigated spatial-spectral domain channels 650-1 . . .650-4 (e.g., near interference-free). A received transmission from anode can appear across one or more receive spatial channels 510-1 . . .510-4, and hence there are a corresponding number of spatial domainchannels 650-1 . . . 650-4, each comprised of multiple (e.g., 32)whitened spectral or frequency channels. For instance, spatial domainchannel 650-1 includes multiple whitened spectral channels (e.g., 32spectral channels), spatial domain channel 650-2 includes multiplewhitened spectral channels (e.g., 32 spectral channels), spatial domainchannel 650-3 includes multiple whitened spectral channels (e.g., 32spectral channels), and spatial domain channel 650-4 includes multiplewhitened spectral channels (e.g., 32 spectral channels). Together, thespatial domain channels 650-1 . . . 650-4 include a number of whitenedspectral-spatial channels. For example, in this non-limiting embodiment,where there are four spatial domain channels 650-1 . . . 650-4 eachhaving 32 spectral channels, there would be 128 whitenedspectral-spatial channels (4 spatial by 32 spectral).

The whitening matrix (W) offers the key linear combinations to mitigateinterference. By judiciously choosing the relevant subset of respectiveeigenvalues {circumflex over (Λ)} and eigenvectors V from theauto-correlation of matrix (Z), the key linear combinations formitigating interference are obtained via W={circumflex over (Λ)}^(−½)V.Whitening in the spectral domain offers the advantage of space-timewhitening at significantly less complexity. Furthermore, channelizationis adaptable to the expected environment.

Each MDFT synthesis bank 660-1 . . . 660-4 can receive one of thespatial-spectral domain channels 650-1 . . . 650-4 from the adaptiveinterference mitigation space-frequency whitener module 640, and performa MDFT synthesis operation on that spatial-spectral domain channel 650-1. . . 650-4 that it receives to generate a time-domain channelizedsignal 670-1 . . . 670-4 of reconstructed beam samples. Each time-domainchannelized signal 670-1 . . . 670-4 represents a respective spatialchannel. Collectively, the time-domain channelized signals 670-1 . . .670-4 output by the MDFT synthesis banks 660-1 . . . 660-4 can outputthe reconstructed beam samples as a time-domain matrix (Y) 670. In otherwords, the MDFT synthesis banks 660-1 . . . 660-4 can re-construct theinterference-mitigated whitened matrix (WZ) 650 back to a time-domainmatrix (Y) 670. In this embodiment, the time-domain matrix (Y) 670 canthen be processed by the multi-channel beamformer module 523 of FIG. 5.

By contrast, in the embodiment of FIG. 3A, dismount node has two receiveantennas 310-1, 310-2, and the multi-channel beamformer module 523 ofFIG. 5 is not present. Therefore, in this embodiment, the multi-userRAKE receiver 324 of FIG. 3A can receive two time-domain channelizedsignals 670-1, 670-2 from MDFT synthesis banks 660-1, 660-2. In otherwords, in the embodiment of FIG. 3A, the time-domain matrix (Y) 670would include time-domain channelized signals 670-1, 670-2 from eachMDFT synthesis bank 660-1, 660-2 that can then be processed by themulti-user RAKE receiver 324. In addition, it should be noted that ifthe dismount node only had a single antenna, then a space-spectrumwhitener 522′ of FIG. 6 is optional and whitening may or may not beapplied depending on the implementation.

Although not illustrated in FIG. 6, in one non-limiting embodiment, thecombination of the multi-channel beamformer module 523, the multi-userRAKE receiver 524 and the maximum likelihood ratio combiner module 526can be referred to as a space-time receive code-based beamformingmodule. Although not illustrated, the space-time receive code-basedbeamforming module can receive space-time signal streams 670-1 . . .670-4 from each MDFT synthesis bank 660-1 . . . 660-4 of FIG. 6, andderive the joint code-based-beamforming matrix (B) across all detectedchannels (e.g., all detected interference mitigated time-domainchannelized signals). The space-time receive code-based beamformingmodule can then apply the joint code-based-beamforming matrix (B) to thetime-domain matrix (Y) 670 to beam combine {tilde over (x)}=BY, thevarious time-domain channels 670-1 . . . 670-4 (e.g., the interferencemitigated time-domain channelized signals). The space-time receivecode-based beamforming module can then select a relevant sub-set of theinterference mitigated time-domain channelized signals to generate abeam combined signal (or joint soft decision represented by vector{tilde over (x)})) that can be processed by the gather, de-interleaveand decoder block 528 of FIG. 5, which, as noted above, performsde-interleaving, forward error correction (FEC) and broadcast decodingon the joint soft decision received from the maximum likelihood ratiocombiner module 526.

Further, as noted above with respect to FIG. 3A, the multi-user RAKEreceiver 324 and the maximum likelihood ratio combiner module 326collectively provide a multi-channel beamformer module that can performdistributed cooperative beamforming. Although not illustrated in FIG. 6,in one embodiment of a dismount node having two receive antennas 310-1,310-2, the multi-channel beamformer module (not illustrated) of adismount node can receive the interference mitigated time-domainchannelized signals 670-1, 670-2 from each MDFT synthesis bank 660-1,660-2 and can derive a joint code-based-beamforming matrix (B) acrossall relevant time-domain channelized signals; apply the jointcode-based-beamforming matrix to the time-domain matrix to beam combinethe time-domain channelized signals; and select a sub-set of thetime-domain channelized signals to generate a beam combined signal. Thesignal of interest (SOI) does not necessarily exist across all thetime-domain channelized signals. Depending upon the channel, the SOI mayonly exist on a subset of the received time-domain channelized signalspace.

FIG. 7 is a table 700 that shows waveform attributes for a range ofmodes and throughput options that are supported in accordance with somenon-limiting examples of the disclosed embodiments. In table 700, column710 shows seven different modes of operation, while column 730illustrates that cooperative broadcast diversity beam combining andmulti-hop transmission are implemented in each of the seven differentmodes of operation from column 710. As noted above, the disclosedembodiments can utilize balanced FH/DSSS hybrid modes to help provide aLow Probability of Intercept/Low Probability of Detection (LPI/LPD)performance. The various examples shown in table 700 illustrate thatthese throughput options can be tailored based on Low Probability ofDetection (LPD) and anti jam mission needs. Adaptive power control andmultiple FEC modes help minimize RF emission.

Column 720 shows corresponding modulation characteristics for each ofthe seven different modes of operation from column 710. The firstsub-column of column 720 indicates that frequency hopping is optionalfor all modes of operation, whereas the second sub-column of column 720indicates that DSSS is used in all modes of operation. The thirdsub-column of column 720 shows a number of OVSF codes used in each ofthe seven different modes of operation from column 710. In this example,one OVSF code is used in modes of operation 1-3 from column 710, whereastwo OVSF codes are used in the 3rd mode of operation from column 710,and four OVSF codes are used in the 4th through 7th modes of operationfrom column 710. The fourth sub-column of column 720 shows the spreadingfactor used in each of the seven different modes of operation fromcolumn 710. In this example, a spreading factor of 32 is used in modesof operation 1-5 from column 710, whereas A spreading factor of 16 isused in the 6th mode of operation from column 710 and a spreading factorof 8 is used in the 7th mode of operation from column 710. The fifth andsixth sub-columns of column 720 show different types of modulation thatcan be used in each of the seven different modes of operation fromcolumn 710. In this example, BPSK modulation is used in the first andsecond modes of operation from column 710, whereas QPSK modulation isused in the 3rd through 7th modes of operation from column 710.

Column 740 shows different physical layer coding rate options for eachof the seven different throughput modes of operation from column 710.The first sub-column of column 740 shows that broadcast coding is usedin each of the seven different modes of operation from column 710. Thesecond sub-column of column 740 shows that a ¼ coding rate is used inthe first mode of operation from column 710, while a ½ coding rate isused in the 2nd and 3rd modes of operation from column 710, and ¾ codingrate is used in the 4th through 7th modes of operation from column 710.

Spectral efficiency is a function of forward error correction (FEC)rate. In one implementation, a 4096 symbol LDPC decoder is used withrates of ¼, ½ and ¾. A ¼ code rate is less spectrally efficient than a ¾code rate and hence has higher detection ratio. The detection ratio isthe ratio of squad-to-base range relative to squad-to-interceptor (orthreat) range. For QPSK modulation, each I/Q rail is processed as aseparate code word. The addition of multiple data channel OVSF furtherincreases spectral efficiency to achieve higher throughput within thesame spectrum. To minimize the processing impact of multiple FECchannels, higher rates only utilize higher coding rates. QPSK uses rate1/2 and ¾ codes, whereas multiple OVSF are QPSK and rate 3/4 only.

Column 770 shows effective information bit rates (in kilobytes/second).Column 770 includes two sub-columns 750, 760. Sub-column 750 showseffective information bit rates (in kilobytes/second) when operating ina hopping mode at 3600 hops/second, while sub-column 760 shows effectiveinformation bit rates (in kilobytes/second) when operating in a singlefrequency mode. As can be seen, the information bit rates supported bythe FH/DSSS waveform can vary depending on the implementation. In thisnon-limiting implementation, the FH/DSSS waveform supports informationrates in the range of 7 kbps-925 kbps through flexible Forward ErrorCorrection (FEC) and structure afforded by DSSS codes. Column 770illustrates that the effective information bit rates (inkilobytes/second) are greater when operating in a single frequency modeas opposed to when operating in a hopping mode at 3600 hops/second.

It is desirable to maximize the detection range ratio (i.e., largerdetection ratios are better). Increasing the hop rate (e.g., shorter hopdwells) increases the detection ratio by requiring higher SNR at theinterceptor. Faster hop rates provide for less integration of the noiseand require higher SNR to maintain the same probability of detection andfalse alarm rate. The effect of increasing hop rate on the communicationlink require larger pilot power to provide channel information requiredfor the RAKE receiver. Lower FEC rates enable lower received SINRoperation, also requiring higher pilot power to provide channelinformation. Lower FEC rate and pilot SINR can be improved by reducingthe hop rate.

As noted above, the hop rate and spreading rate of the FH/DSSS waveformcan be selected to depending on the implementation. To help facilitate,low probability of intercept/low probability of detection (LPI/LPD)signaling, the proposed waveform is a hybrid FH/DSSS waveform hopping ata hop rate (kilohops/second) and simultaneously spreading at a certainchip rate (Megachips/second). For instance, in one implementation, theprotected FH/DSSS waveform operates at 2.5 megachips/second (Mcps) andup to 10 kilohops/second, with a DSSS spreading factor of 32, 16 or 8.

Anti jam performance is a function of the jamming waveform and mode ofoperation. Low Probability of Detection (LPD) waveforms by their verynature defeat follower jammers. Anti jamming performance improves withincreasing the number of hop frequencies and with reduction in datarate. The disclosed embodiments can help to provide anti jamcommunications by providing several different fast frequency hoppingmodes for the best anti jam performance. Joint spectral-spatialwhitening helps provide anti jam and interference mitigation. Adaptivespace-spectrum whitening on channelized spectrum provides performance ofspace-time whitening at significantly less complexity, and helps providelow risk interference/jammer mitigation. As shown in FIG. 7, the highestanti-jam performance is achieved with Mode 1, 7 kbps, operating at thehighest hop rate, across the largest available spectrum.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention. It being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims.

What is claimed is:
 1. A node configured to communicate in a cooperativebroadcast multi-hop network that employs broadcast flood routing andmulti-hop transmission using a direct-sequence spread-spectrum (DSSS)waveform, the node comprising: a first antenna configured to receive afirst plurality of DSSS signals from other nodes on a first particularchannel, and output a first channel that includes the first plurality ofDSSS signals, wherein the first plurality of DSSS signals includetransmissions that are directly received from other nodes and multi-pathcomponents of those transmissions; a second antenna configured toreceive a second plurality of DSSS signals from the other nodes on asecond particular channel, and output a second channel that includes thesecond plurality of DSSS signals, wherein the second plurality of DSSSsignals include transmissions that are directly received from the othernodes and multi-path components of those transmissions; and a waveformmodule having a receiver processing chain comprising: an adaptivespace-spectrum whitener (ASSW) module that is configured to: performadaptive space-spectrum whitening to detect and remove interferencesignals received from each of the first and second channels byperforming a covariance analysis to generate a plurality of channelizedsignals comprising: a first channelized signal that comprisestransformed beam samples for the first channel and a second channelizedsignal that comprises transformed beam samples for the second channel,wherein the ASSW module comprises: a modified Discrete Fourier Transform(MDFT) analysis module comprising: a plurality of an MDFT analysisbanks, wherein each MDTF analysis bank corresponds to one of the firstand second antennas and is configured to: receive a beam from one of thefirst and second antennas in the spectral domain, wherein each beamcomprises a digitized spatial stream of frequency channelized RF samplesthat are digitized to preserve spatial diversity; and channelize thebeam to generate a channelized beam of frequency samples, wherein eachchannelized beam comprises multiple spectral channels, wherein thechannelized beams collectively comprise a number of spectral-spatialchannels equal to the product of the number of channelized beams and themultiple spectral channels, wherein the channelized beams collectivelyform a spatial-spectral matrix (Z) of time-frequency samples across thedifferent antennas; an adaptive interference mitigation space-frequencywhitener module configured to: apply a whitening matrix (W) to thespatial-spectral matrix (Z) to remove interference and generate aninterference-mitigated whitened matrix (WZ) that comprises a pluralityof interference-mitigated spatial-spectral domain channels; and a MDFTsynthesis module comprising: a plurality of MDFT synthesis banks thatcollectively re-construct the interference-mitigated whitened matrix(WZ) back to a time-domain matrix (Y) that comprises a plurality ofinterference mitigated time-domain channelized signals, wherein eachMDFT synthesis bank is configured to perform a MDFT synthesis operationon one of the spatial-spectral domain channels to generate aninterference mitigated time-domain channelized signal of reconstructedbeam samples, wherein each interference mitigated time-domainchannelized signal represents a respective spatial channel; and amulti-user RAKE receiver is configured to: combine, when performingdemodulation processing, the plurality of interference mitigatedtime-domain channelized signals to generate a subset (1 . . . F) offingers that combine components of a plurality of transmissions directlyreceived from the other nodes and multipath components of transmissionsreceived from the other nodes.
 2. The node according to claim 1, whereineach row of the spatial-spectral matrix (Z) represents spatial-spectralsamples unique to one of the channelized beams, and wherein each columnof the spatial-spectral matrix (Z) represents time indices.
 3. The nodeaccording to claim 2, wherein the adaptive interference mitigationspace-frequency whitener module is configured to calculateauto-correlation matrices across rows of the spatial-spectral matrix (Z)such that the resulting whitened matrix (WZ) is a diagonal correlationmatrix.
 4. The node according to claim 1, wherein the receiverprocessing chain further comprises: a de-hop module configured to:de-hop each of the received DSSS signals by tuning to a particularfrequency to receive each DSSS signal and then channelizing inputspectrum for each of the received DSSS signals to generate beam samplesfor each channelized signal.
 5. The node according to claim 1, whereinthe multi-user RAKE receiver comprises: first and second correlationmodules each being configured to receive the first and secondchannelized signals output by the ASSW module, wherein each of the firstand second channelized signals is a spatial stream, wherein each of thefirst and second correlation modules comprises: correlator blocks foreach of the plurality of nodes (1, . . . , N), wherein each correlatorblock is driven by a unique scramble code that identifies transmissionsfrom a particular node and performs correlation for that particular nodeby processing a spatial stream received from the ASSW module and theunique scramble code for that particular node to determinechannel-multipath correlations and generate one or more candidatefingers multipath location and respective complex weight, wherein eachfinger corresponds to a specific channel-signal pair for that particularnode or a specific channel-multipath component pair for that particularnode; and a finger selection module configured to receive the fingersoutput from each correlator block and to select the subset (1 . . . F)of the fingers having sufficient correlation by selecting which nodescontribute to the F total largest signal multipath components received.6. The node according to claim 5, wherein the unique scramble code is afirst code that is unique for that particular node that is logicallycombined with a security code.
 7. The node according to claim 5, whereinthe waveform module further comprises: a maximum likelihood ratiocombiner module configured to: maximally ratio combine aligned symbolsfor each of a subset (1 . . . F) of fingers on a per channel basis togenerate a soft decision across each of the multiple channels; andcombine the soft decisions into a joint soft decision.
 8. The nodeaccording to claim 7, wherein the maximum likelihood ratio combinermodule comprises: a plurality of processing modules comprising: aprocessing module for each of the other nodes that processes signals forthat node, wherein each processing module comprises: a coherent combinemodule for that node that is configured to receive a number of thesubset of fingers from the finger selection module, and coherentlycombine that number of the subset of fingers to generate an outputsignal; a descrambler for that node that is configured to descramble theoutput signal received from that coherent combine module using a uniquedescramble code for that node to generate a descrambled signal; and apilot despreader module for that node that is configured to despread thedescrambled signal to generate a despread pilot signal; and a coherentcombiner module that is configured to coherently combine, using pilotsoft-decision bits from each of the despread pilot signals for each nodeof the other nodes, each of the descrambled signals received acrossmultiple nodes to generate a coherently constructed signal of spreaddata channels that comprise a coherently combined vector of chips ofinformation; and wherein the waveform module further comprises: a datadespreader module configured to despread and convert the chips from therespective data channels to generate demodulated data symbols that areconverted into data soft-decision bits; and a gather, de-interleave anddecoder block configured to: a gather block configured to concatenatethe data soft-decision bits from each hop across multiple received hopstogether to form codeword soft-decision bits; a de-interleaver blockconfigured to de-interleave the codeword soft-decision bits; and adecoder block configured to perform low density parity check (LDPC)forward error correction (FEC) decoding and broadcast decoding on thecodeword soft-decision bits to recover information bits corresponding tothe complete codeword.
 9. The node according to claim 1, wherein thewaveform module further comprises: a maximum likelihood ratio combinermodule that along with the multi-user RAKE receiver collectivelyprovides: a multi-channel beamformer module being configured to performcooperative beamforming on a per channel basis by processing thetime-domain matrix (Y) and coherently combining a subset oftransmissions and multipath components for each transmission that arereceived from other nodes together, wherein the subset of transmissionsand multipath components are those having signal strength greater thanor equal to a threshold, and wherein coherently combining isaccomplished by time aligning the respective signals of interest, andremoving frequency offset and phase offset from each transmission. 10.The node according to claim 9, wherein the multi-channel beamformermodule is configured to: receive the interference mitigated time-domainchannelized signals from each MDFT synthesis bank; derive a jointcode-based-beamforming matrix (B) across all detected interferencemitigated time-domain channelized signals; apply the jointcode-based-beamforming matrix to the time-domain matrix to beam combinethe interference mitigated time-domain channelized signals; and select asub-set of the interference mitigated time-domain channelized signals togenerate a beam combined signal.
 11. The node according to claim 1,wherein the node further comprises: a third antenna and a fourthantenna, the third antenna being configured to receive a third pluralityof DSSS signals from other nodes on a third particular channel, andoutput a third channel that includes the third plurality of DSSSsignals, the fourth antenna being configured to receive a fourthplurality of DSSS signals from other nodes on a fourth particularchannel, and output a fourth channel that includes the fourth pluralityof DSSS signals, wherein the third and fourth plurality of DSSS signalseach include transmissions that are directly received from other nodesand multi-path components of those transmissions, wherein the first,second, third and fourth antennas are part of a multi-band phasedantenna array having a number (N) of antennas that include the first,second, third and fourth antennas; and wherein the receiver processingchain of the waveform module further comprises: a space-time receivecode-based beamforming module, comprising: a multi-channel beamformermodule being configured to: perform adaptive beamforming on a perchannel basis, wherein the multi-channel beamformer module performs amatrix operation that linearly transforms interference mitigatedtime-domain channelized signals to coherently combine the interferencemitigated time-domain channelized signals into a smaller number (NT) ofdirectional beams; the multi-user RAKE receiver being configured toprocess each of the directional beams output by the multi-channelbeamformer module and align symbols using scramble code correlation; anda maximum likelihood ratio combiner module.
 12. The node according toclaim 11, wherein the multi-channel beamformer module is configured to:receive the interference mitigated time-domain channelized signals fromeach MDFT synthesis bank; derive a joint code-based-beamforming matrix(B) across all detected interference mitigated time-domain channelizedsignals; apply the joint code-based-beamforming matrix to thetime-domain matrix to beam combine the interference mitigatedtime-domain channelized signals; and select a sub-set of theinterference mitigated time-domain channelized signals to generate abeam combined signal.
 13. The node according to claim 11, wherein thetransmissions received across each of the number (N) of antennas of themulti-band antenna array are coherently combined on a per channel basisto generate a corresponding directional beam, wherein each directionalbeam covers a portion of an azimuth range.
 14. The node according toclaim 11, wherein node further comprises: a power control module that isconfigured to: encode originating transmit power in a message to supportadaptive power control and encode channel status information in themessage so that channel status of the cooperative broadcast multi-hopnetwork is propagated to each of the other nodes of the cooperativebroadcast multi-hop network; and wherein the node, when transmitting asan original sender of a transmission, is configured to broadcast aparticular message on odd numbered hop intervals to propagate theoriginating transmit power channel status information to the other nodesin the cooperative broadcast multi-hop network.
 15. The node accordingto claim 14, wherein each of the other nodes that receive the particularmessage is configured to: process the channel status information toestimate a receive signal-to-noise (SNR); determine, based on theestimated receive SNR and the originating transmit power, whethertransmit power of that node should be adjusted before transmitting orrelaying a message; and when it is determined that transmit power ofthat node is to be adjusted: adjust current transmit power of that node;and re-transmit messaging including current transmit power on evennumbered hop intervals.
 16. The node according to claim 14, wherein theparticular message is one or more of: a push-to-talk (PTT) message; anda synchronization message that is regularly broadcast a synchronizationchannel to maintain time synchronization relative to a master node sothat transmissions of the nodes are synchronized to arrive within a samereception window of the multi-user RAKE receiver.
 17. The node accordingto claim 1, wherein the DSSS waveform is a frequency-hoppingdirect-sequence spread-spectrum (FH/DSSS) waveform in which DSSSmodulation is combined with frequency hopping (FH) between DSSS channelsto provide a hybrid FH/DSSS modulation format, and wherein the FH/DSSSwaveform has a hop rate and a spreading rate that are adjustable, andwherein the node further comprises: a beamformer and hop assignmentmodule comprising: a hop assignment module that includes aFast-Frequency Hopping (FFH) transmitter that is configured to assign ahop number for transmissions by that node, wherein a hop number is afunction of time, and a hop frequency is based on pseudo-randomsequence; and a beamformer module that is configured to update amplitudeand phase weightings of a DSSS signal that is provided to the two ormore antennas.
 18. The node according to claim 1, wherein the nodecomprises: a different interleaver module than the other nodes.
 19. Thenode according to claim 1, wherein the node is configured to: transmittransmissions that are modulated using: a unique scramble code for thatnode that identifies transmissions from that node to distinguish themfrom transmissions by other nodes that are part of the cooperativebroadcast multi-hop network and a common scramble code that is sharedwith the other nodes, wherein each transmission by the node is adirect-sequence spread-spectrum (DSSS) signal having DSSS waveform;broadcast transmissions on a unique channel for that node whentransmitting as an original sender of a transmission, wherein the uniquechannel for the node is defined by an odd numbered hop interval assignedto that node and the unique scramble code assigned to that node; andre-transmit, when operating as a relay node, any transmissions that arereceived error free from the other nodes on another unique channel forthat node that is defined by an even numbered hop interval assigned tothat node and the unique scramble code assigned to that node.
 20. Thenode according to claim 1, wherein the node is configured to: receivetransmissions from other nodes that are original senders and multipathcomponents thereof on odd numbered hop intervals; and receivere-transmitted transmissions from other nodes that are relays andmultipath components thereof on even numbered hop intervals.